for pharma & med tech prelims

8/6/2019 For Pharma & Med Tech Prelims

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CHEMICAL BONDING The TRANSFER or SHARING of electrons.

In the formation of chemical compounds from elements, valence electronsare usually either:

a. transferred from the outer shell of one atom to the outer shell of another atomand

b. shared among the outer shells of the combining atoms.

Ways to PRODUCE A CHEMICAL BOND:1) IONIC BONDING~ transfer of electrons from one atom to another.

The compound formed is called IONIC COMPOUND & the type of bond formedis an IONIC BOND.Usually metals + non-metals produce ionic bonds. The compds they produce arevast crystal lattices.Ex. 11 Na + 17 Cl NaCl

Electronic Configuration: Na 1s 2 2s 2 2p 6 3s 1

Cl 1s 2 2s 2 2p 6 3s 2 3p 5

..Electron Dot Formula: Na Cl :

.. Na atom losses 1 e, while Cl atom accepts to follow the octet rule.Na atom becomes Na ion (cation)Cl atom becomes Cl ion (anion)

IONS ~ are charged particles created when atoms either LOSE or GAIN ELECTRONS.

CATIONS ~ are positively charged ions. Usually METALS.ANIONS ~ are negatively charged ions. Usually NON-METALS.

IONIZATION ENERGY ~ the energy needed to remove an electronin an atom.

2) COVALENT BONDING ~ sharing of electrons between two atoms,usually non-metals.

The type of bond formed is the COVALENT BOND & they produce CovalentCompounds.Usually non-metals + non-metals produce covalent bonds.Ex. 1H + 1H H2

Electronic Configuration: H: 1s 1

H: 1s 1


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Electron Dot Formula: H + H H : H

MOLECULE~ a chemical structure held together by Covalent Bonds.

SELF TEST:1) Show the formation of a chemical bond of the following:

a. Magnesium Bromide (MgBr 2) d. N 2b. O 2 e. NaClc. Al 2S 3 f. H 2 SO 4

3) MULTIPLE BONDING ~ a bond of electrons attained in severaltypes of bonding such as:a) Single Covalent Bond attained in a single pair.

Ex: H + H H : H or H H or H 2

b) Double Covalent Bond when 2 pairs of electrons aresharing between 2 nuclei represented by 2 dashes ( = )

Ex. CO 2c) Triple Covalent Bond when 3 pairs of electrons are

sharing & represented by 3 dashes ( = ) .Ex. Nitrogen (N 2) ~ is found in the atmosphere as a diatomic

molecule. Each N atom has 5 valence electrons & need to share 3electrons. The 3 shared pair electrons will form a triple bond by 3 dashes.Accounts for 80% of the of the gases in the atmosphere, stable; relativelyUNREACTIVE. Because of being unreactive, Nitrogen is in the form of N 2,useless to most forms of life. There is only 1 type of organism that utilizethe atmospheric nitrogenBACTERIA. They live on soil or in roots of plants such as peas & alfalfa. Rootscontains NODULES

these nodules contain the Nitrogen-Fixing Bacteria. Using the nutrient provided throughthe roots, these bacteria CONVERT the Nitrogen in the air to form AMMONIA (NH 3) or NITRATES (NO 3). These compds w/c resulted upon conversion of the Nitrogen insidethe roots to become compds that can be used by plants & animals then get N 2 by eating

the plant.Nitrogen has 5 valence e -

CHEMICAL FORMULAA combination of elemental symbols and subscript numbers that is used to show

the composition of a compound depending on the type of compound that the formula


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represents, the information that it provides will vary slightly whether it is a molecular compound or an ionic compound.

TYPES OF CHEMICAL FORMULA:1. Molecular Formula A chemical formula that denotes the constituent

elements of a molecular substance & the # of atoms of each elementcomposing 1 molecule.

Ex. C 6 H6 (benzene) H 2O 2 (hydrogen peroxide)

2. Empirical Formula A special type of chemical formula,that shows the composition of a molecule not as itactually exists, but in a simple whole number ratio.

Ex. CH HO

Ionic compounds are composed of charged ions that are heldtogether by electrostatic forces. A typical type of ionic compound, called abinary compound because it is made up of two elements , will be composedof metallic positive ions ( cations ) and nonmetal negative ions ( anions ).Another type of ionic compound, called a ternary compound as it contains threeelements , is composed of monatomic ions and polyatomic ions. When dealingwith ionic formulas it is very important to remember that the formula does notshow how the compound actually exists in nature. It only shows the ratio bywhich the individual ions combine.

Ex. The ionic formula for calcium chloride is CaCl 2. Since calcium chloride is an ionic

compound, this formula does not mean that there are actually two chlorine atomsfloating around attached to one calcium atom. Ionic compounds are actuallycontinuous, lacking the discrete units that make up a sample of a molecular substance.Rather, the formula shows that a sample of calcium chloride contains twice as manychlorine atoms as calcium atoms. Remember that ionic compounds are notmolecules , so the formula CaCl 2 is said to represent one formula unit of calciumchloride.

Molecular compounds are held together by covalent bonds, or shared pairs of electrons. Molecular formulas do show these molecules as theyactually exist as discrete units in nature.

Ex. When we say that the molecular formula of water is H 2O, we can see that themolecules of water are made up of three atoms; two hydrogen atoms are covalentlybonded to each oxygen atom.

Isomerism - is the phenomenon whereby certain compounds, with the samemolecular formula, exist in different forms owing to their different organisations of atoms. The concept of isomerism illustrates the fundamental importance of molecular


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structure and shape in organic chemistry. Isomers are molecules that have the samechemical formula but different structural formulas.

CH 3CH 2 CH 2 CH 2 CH 2CH3or C 6H14 or hexane

CH 3

I

CH 3 CH 2 CH CH 2 CH 3or Hexane

Structural Isomerism

Structural Isomers have different structural formulae because their atoms are linkedtogether in different ways.

It arises owing to: arrangement of Carbon skeleton


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e.g. The formula C 4H10 represents two possible structuralformulae, butane and methylpropane :

position of Functional group

e.g. propan-1-ol and propan-2-ol

different Functional groups

e.g. the molecular formula C 2H60 representsboth ethanol and methoxymethane .


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ethanol Dimethyl ether ethyl alcohol, pure alcohol, grain alcohol IUPAC: methoxymethaneor drinking alcohol

Cyclic alkanes are isomeric with alkenes, e.g. cyclopropane and propene

FUNCTIONAL GROUPOrganic Chemistry Essentials

Many important organic chemistry molecules contain oxygen or nitrogen. It's a goodidea to memorize the names and structures of these functional groups .
http://chemistry.about.com/od/organicchemistry/ig/Functional-Groups/http://chemistry.about.com/od/organicchemistry/ig/Functional-Groups/


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Benzyl acetateHas an ester functional group (in red) , an acetyl moiety (circledwith green) and a benzyl alcohol moiety (circled with orange) .Other divisions can be made.

In organic chemistry, functional groups -- are specific groups of atoms withinmolecules that are responsible for the characteristic chemical reactions of thosemolecules. The same functional group will undergo the same or similar chemicalreaction(s) regardless of the size of the molecule it is a part of. However, its relativereactivity can be modified by nearby functional groups.

The word moiety is often used synonymously to "functional group," but, according to theIUPAC definition, a moiety -- is a part of a molecule that may include functional groupsas substructures. For example:

ester

A carboxylic acid ester.

R and R' denote any alkyl ( or aryl (functional)groupEsters are usually derived from an inorganic acid or organic acid in which at least one-OH (hydroxyl) group is replaced by an -O-alkyl (alkoxy) group, and most commonlyfrom carboxylic acids and alcohols.

Is divided into an alcohol moiety and an acyl moiety, but has an ester functional group.Also, it may be divided into carboxylate and alkyl moieties.

Combining the names of functional groups with the names of the parent alkanesgenerates a powerful systematic nomenclature for naming organic compounds.

The atoms of functional groups are linked to each other and to the rest of the moleculeby covalent bonds. When the group of atoms is associated with the rest of the molecule
http://en.wikipedia.org/wiki/Alkylhttp://en.wikipedia.org/wiki/Arylhttp://en.wikipedia.org/wiki/File:FG-vs-moiety.pnghttp://en.wikipedia.org/wiki/Alkylhttp://en.wikipedia.org/wiki/Aryl


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primarily by ionic forces, the group is referred to more properly as a polyatomic ion or complex ion. ( POLYATOMIC IONS ~ a group of covalently bonded atoms, that

as a group, carries an electrical charge,but since it is so stable, it can throughmost chem. rxns as a unit wont come

apart.) And all of these are called radicals, by a meaning of the term radical that predates thefree radical.

The first carbon atom after the carbon that attaches to the functional group is called thealpha carbon; the second, beta carbon, the third, gamma carbon, etc. If there is another functional group at a carbon, it may be named with the Greek letter, e.g. the gamma-amine in gamma-aminobutanoic acid is on the third carbon of the carbon chain attachedto the carboxylic acid group.

IIThe HYDROCARBONS

In Organic Chemistry it is the simplest organic compound consisting entirely of hydrogen and carbon.

Hydrocarbons from which one hydrogen atom has been removed are functional groups,called -- hydrocarbyls. (organic chemistry) Any univalent radical, derived from ahydrocarbon, such as methyl or phenyl. Aromatic hydrocarbons (arenes), alkanes,alkenes, cycloalkanes and alkyne-based compounds are different types of hydrocarbons.

The majority of hydrocarbons found naturally occur in crude oil, where decomposedorganic matter provides an abundance of carbon and hydrogen which, when bonded,can catenate -- to form atoms of the same chemical element into a chain held together by chemical bonds.

A) AlkanesOrganic Chemistry Nomenclature & Numbering


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A saturated hydrocarbon in which all of the carbon-carbon bonds are single bonds .Each carbon atom forms four bonds and each hydrogen forms a single bond to acarbon. The bonding around each carbon atom is tetrahedral, so all bond angles are109.5. As a result, the carbon atoms in higher alkanes are arranged in zig-zag rather than linear patterns.

Straight Chain Alkanes Here is a table that gives the names of the straight chainalkanes. It's a good idea to commit this table to memory. The general formula for analkane is C nH2n+2 where n is the number of carbon atoms in the molecule. There are twoways of writing a condensed structural formula. For example, butane may be written asCH 3CH 2CH 2CH 3 or CH 3(CH 2)2CH 3.

# Carbon Name Molecular Formula

StructuralFormula

1 Methane CH 4 CH 4

2 Ethane C 2H6 CH 3CH 3

3 Propane C 3H8 CH 3CH 2CH 3

4 Butane C 4H10 CH 3CH 2CH 2CH 3

5 Pentane C 5H12 CH 3CH 2CH 2CH 2CH 3

6 Hexane C 6H14 CH 3(CH 2)4CH 3

7 Heptane C 7H16 CH 3(CH 2)5CH 3

8 Octane C 8H18 CH 3(CH 2)6CH 3

9 Nonane C 9H20 CH 3(CH 2)7CH 3

10 Decane C 10 H22 CH 3(CH 2)8CH 3

Rules for Naming Alkanes

The parent name of the molecule is determined by the number of carbons in thelongest chain.

In the case where two chains have the same number of carbons, the parent is thechain with the most substituents.

The carbons in the chain are numbered starting from the end nearest the firstsubstituent. In the case where there are substituents having the same number of carbons from

both ends, numbering starts from the end nearest the next substituent. When more than one of a given substituent is present, a prefix is applied to

indicate the number of substituents. Use di- for two, tri- for three, tetra- for four,etc. and use the number assigned to the carbon to indicate the position of eachsubstituent.
http://chemistry.about.com/library/glossary/bldef528.htmhttp://chemistry.about.com/library/glossary/bldef528.htm


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Branched Alkanes Branched substituents are numbered starting from the carbon of the substituent

attached to the parent chain. From this carbon, count the number of carbons inthe longest chain of the substituent. The substituent is named as an alkyl groupbased on the number of carbons in this chain.

Numbering of the substituent chain starts from the carbon attached to the parentchain.

The entire name of the branched substituent is placed in parentheses, precededby a number indicating which parent-chain carbon it joins.

Substituents are listed in alphabetical order. To alphabetize, ignore numerical(di-, tri-, tetra-) prefixes (e.g., ethyl would come before dimethyl), but don't ignoredon't ignore positional prefixes such as iso and tert (e.g., triethyl comes beforetertbutyl).

Conformations of Alkanes

Conformations are different forms of a molecule, related by simple rotation about asingle bond. Such interconversion are usually very rapid, so that a sample of a givenmolecule may exist in many different conformations.

For ALKANES , various conformations can be represented by using dash-wedgenotation in a structural "perspective" drawing. An alternate depiction is a NewmanProjection , which views a molecule by looking down a C-C bond axis, showing therelative orientation of groups off the two carbon atoms.

Ethane

This conformation of ethane is the staggered form. The various hydrogen atoms on thetwo carbons form a dihedral angle of 60.


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This conformation of ethane is the eclipsed form. The hydrogen atoms have a dihedralangle of 0.

The staggered conformation of ethane is more stable than the eclipsed form by 12.1kJ/mol, so that as one methyl group rotates 360 relative to the other, the compoundpasses through three stable staggered conformers via three unstable eclipsed forms.This barrier is small enough that at 25C the compound changes conformation about 50million times each second!

Butane

Butane has not only eclipsed and staggered conformations , but also forms that varyin the relative orientation of the methyl groups.

anti eclipsed gauche fully eclipsed

fully eclipsed


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Relative energy:0 kJ/mol +15.9 kJ/mol +3.8 kJ/mol

anti eclipsed gauche

+18.8 kJ/mol

fully eclipsed

As with ethane, the eclipsed conformations are higher energy than the staggered. Thestaggered conformation where the two methyl groups are as far away from one another as possible (with a dihedral angle of 180, seen in the Newman projection) is calledthe anti conformation, and is the lowest-energy arrangement. The two staggered formswith the methyl groups in closer proximity (60) are the gauche conformations. Direct


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interconversion of one gauche form to the other requires passing through the highest-energy eclipsed form, where the two methyl groups are next to each other. A space-filling representation of this conformation shows that the methyl groups are physicallytouching, leading to the high energy.

Alkanes: Natural SourcesThe alkanes are isolated from natural gas and petroleum. Natural gas contains mainlymethane, with smaller amounts of other low-molecular-weight alkanes. Petroleum,which is a complex mixture of many compounds, is the main source of all other alkanes.The lighter fractions are distilled from the mixture to produce the liquid alkanes, whilethe residue from the distillation produces the solid alkanes.

By far the most important economic use for alkanes is their use as fuels, an ingredientin kerosene. They are also used as lubricants and as non-polar solvents. They arelargely unreactive, but can react with halogens such as bromine in the presence of sunlight to form halogenoalkanes, which are much more useful in organic synthesis.

Alkanes are used in hundreds of products such as plastics, paints, drugs, cosmetics,detergents, insecticides and many more. Environmental hazards and health risk of common liquid perfluoro-n-alkanes & a potent greenhouse gases. These liquidperfluoro-n-alkanes tend to be hydrophobic and partitioned into organic matter, and theyhave exceptionally low solubility in water and extremely high vaporization from the water bodies, suggesting that it will sink into the atmosphere if it is released into theenvironment.

PHYSICAL PROPERTIES:Alkanes are non-polar


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Intermolecular forces are van der Waals forcesInsoluble in water Less dense than water

CHEMICAL PROPERTIES:Combustion of Alkanes

All Alkanes burn in air to give Carbon Dioxide & Water

Alkanes: Preparations

Alkanes are rarely prepared from other types of compounds because of economicreasons. However, ignoring financial considerations, alkanes can be prepared fromthe following compounds:

1. Unsaturated compounds via catalytic reduction

2. Alkyl halides via coupling (Wurtz reaction)


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3. Alkyl halides via Grignard reagent

4. Alkyl halides via reduction

Methyl Chloride Methane

Although organic chemists refer to the above diagrams as equations, they

are not balanced. In addition, not every product formed is shown. These

diagrams are really reaction schemes.

5. Combustion of methane

CH 4 + 2O 2 CO 2 + 2H 2O


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6. Alkanes: Halogenation

The reaction of a halogen with an alkane in the presence of ultraviolet (UV)

light or heat leads to the formation of a haloalkane (alkyl halide). An example is

the chlorination of methane.

7. Alkanes: Oxidation (Combustion)

Alkanes can be oxidized to carbon dioxide and water via a free-radical mechanism.

The energy released when an alkane is completely oxidized is called the heat of

combustion. For example, when propane is oxidized, the heat of combustion is 688

kilocalories per mole.

CH 3CH 2CH 3 + 5O 2 3CO 2 + 4H 2O + energy

CYCLOALKANE

Cycloalkanes are very similar to the alkanes in reactivity, except for the very small ones- especially cyclopropane. Cyclopropane is much more reactive than you would expect.

The reason has to do with the bond angles in the ring. Normally, when carbon formsfour single bonds, the bond angles are about 109.5. In cyclopropane, they are 60.


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With the electron pairs this close together, there is a lot of repulsion between thebonding pairs joining the carbon atoms. That makes the bonds easier to break.

Cycloalkanes are very similar to the alkanes in reactivity, except for the very small ones- especially cyclopropane. Cyclopropane is much more reactive than you would expect.

Cycloalkanes again only contain carbon-hydrogen bonds and carbon-carbon singlebonds, but this time the carbon atoms are joined up in a ring. The smallest Cycloalkaneis cyclopropane. Of cyclohexane is formed known as the "boat" form. In thisarrangement, both of these atoms are either pointing up or down at the same time.

If you count the carbons and hydrogens, you will see that they no longer fit the generalformula C nH2n+2 . By joining the carbon atoms in a ring, you have had to lose twohydrogen atoms.

You are unlikely to ever need it, but the general formula for a cycloalkane is C nH2n .


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Don't imagine that these are all flat molecules. All the cycloalkanes from cyclopentaneupwards exist as "puckered rings".

Cyclohexane, for example, has a ring structure which looks like this:

This is known as the "chair" form of cyclohexane - from its shape which vaguelyresembles a chair.

IIIB) Alkenes

The second class of simple hydrocarbons that consists of molecules that containat least one double-bonded carbon pair. Alkenes follow the same naming conventionused for alkanes . A prefix (to describe the number of carbon atoms) is combined withthe ending "ene" to denote an alkene. The simplest alkene which has the International

Union of Pure and Applied Chemistry (IUPAC) is properly named Ethene, is the two-carbon molecule that contains one double bond but is almost universally known by itscommon name, ethylene( C 2H4). The chemical formula for the simple alkenes followsthe expression C nH2n . Because one of the carbon pairs is double bonded, simplealkenes have two fewer hydrogen atoms than alkanes.

Ethene

Alkenes are also called olefins (an archaic synonym, widely used in the petrochemicalindustry). Aromatic compounds are often drawn as cyclic alkenes , BUT their structureand properties are different and they are not considered to be alkenes.

Carbon-carbon double bonds

Names end in -eneH2C=CH 2 ethene (ethylene)H2C=CH-CH 3 propene (propylene)

cyclohexene
http://www.visionlearning.com/library/pop_glossary_term.php?oid=1585&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1518&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1587&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1586&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1509&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1585&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1518&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1587&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1586&l=http://www.visionlearning.com/library/pop_glossary_term.php?oid=1509&l=


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Each carbon atom in ETHYLENE is attached not to four other atoms, as is the carbon inmethane or ethane, but to three. It seems we will need a different bonding rationale with

which to describe Nature now. Our strategy will be to develop a bonding scheme for thesimplest trivalent compound of carbon, methyl (CH 3 ), and then extend it to ethylene , inwhich each carbon is attached not to three hydrogens as in methyl, but to twohydrogens and the other methylene (CH 2 ) group .

H H H

C H C C

H H HReplacement of one hydrogen in methyl (CH 3), with a methylene (CH 2) group leads tothe framework of ethylene (H 2CCH 2). Note that each carbon so far has only threebonds. In this drawing the full bonding scheme for ethylene is not yet in place.

IUPAC Naming of AlkenesThe rules for naming alkenes are basically the same as those of alkanes but with twodifferences. (1)The parent chain must include the double bond even if it makes it shorter than the others. (2)And the parent alkene chain must be numbered from whichever end gives the first carbon of the double bond the lower of two possible numbers . Also, thelocation number should be given as to where the double bond is (except ethene or

propene, where the location will always be 1). For example:

CH3CH2CH=CH24 3 2 11-butene

CH3CH=CHCH31 2 3 42-butene

CH3 CH3| |

CH3CH2CHCH2CH=CCH37 6 5 4 3 2 12,5-dimethyl-2-heptene

Alkanes which have two double bonds are dienes , those with three are trienes , and soforth. Each double bond has to be located by a number.

CH 2=CHCH=CHCH 31 2 3 4 51,3-pentadiene

CH 2=CHCH 2CH=CH 21 2 3 4 5

1,4-pentadiene

CH 2=CHCH=CHCH=CH 21 2 3 4 5 61,3,5-hexatriene

* alkynes also follow similar naming conventions *

Geometric Isomerism among the Alkenes


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There is no free rotation of a double bond. Doing so would break it. Therefore, manyalkenes exhibit geometric isomerism. For example, cis -2-butene and trans -2-buteneare geometric isomers. Cis means "on the same side," while trans means "on oppositesides."

CH 3 CH 3\ /

C = C/ \

H Hcis -2-butene

CH 3 H\ /

C = C/ \H CH 3

trans -2-butene

Generally, the differences in physical properties are measurable, but their chemicalproperties are very similar.

Different Reactions of Alkenes:

Alkenes are relatively stable compounds, but are more reactive than alkanes due to thepresence of a carbon-carbon pi-bond. The majority of the reactions of alkenesinvolve the rupture of this pi bond, forming new single bonds.

Alkenes serve as a feedstock for the petrochemical industry because they canparticipate in a wide variety of reactions.

1) Addition Reactions of Alkenes

Alkenes are Lewis bases (electron pair donors) because the bond of the carbon-carbon double bond is projected outward where electron-seeking reactants are able toget it. They will react very readily with Lewis acids (electron pair acceptors) and strongBrnsted acids (proton donors). The addition reactions of alkenes make pieces of areactant become separately attached to the carbons at the ends of a double bond.Ethene readily reacts with hydrogen chloride to make 1-chloroethane:

H H H H + H H \ / | | | |

C = C + H-Cl ==> H-C-C-H + Cl - ==> H-C-C-H / \ | | | |H H H H Cl


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CH 2=CH 2 + H-Cl ==> CH 3-CH 2+ + Cl - ==> CH 3-CH 2-Clethyl carbocation

(exists for short duration)

2) Addition of Sulfuric Acid Reaction Another reaction involves ethene and water, giving ethanol (ethyl alcohol), whilesulfuric acid acts like a catalyst called the.

H H H H + H H\ / | | | |C = C + H2SO4 + H2O ==> H-C-C-H + HSO4- + H2O ==> H-C-C-H/ \ | | | |H H H H OHethene water

+ HSO4- + H+ ==> C 2H 5OH + H 2SO 4ethanol

3)Hydrogenation--Addition of Hydrogen

Hydrogenation of alkenes produces the corresponding alkanes. When an alkene ishydrogenated, it becomes and alkane. The reaction is carried out under pressure in thepresence of a metallic catalyst. It requires a catalyst--powdered platinum, for example--Common industrial catalysts are based on platinum, nickel or palladium and often highheat and pressure. This is the hydrogenation of 2-butene:

Pt CH 3CH=CHCH 3 + H-H ==> CH 3CH-CHCH 3 or CH 3CH 2CH 2CH 3

2-butene | |H H

butane
http://library.thinkquest.org/3659/reference/glossary.html#catalysthttp://library.thinkquest.org/3659/reference/glossary.html#catalyst


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Another is for laboratory syntheses, Raney nickel (an alloy of nickel andaluminium) is often employed. The simplest example of this reaction is the catalytichydrogenation of ethylene to yield ethane:

CH2=CH2 + H2 CH3-CH3 ethylene ethane

4) HalogenationIn electrophilic halogenation , the addition of elemental bromine or chlorine toalkenes yields vicinal dibromo- and dichloroalkanes, respectively. The decolorationof a solution of bromine in water is an analytical test for the presence of alkenes:

CH 2=CH 2 + Br 2 BrCH 2-CH 2Br Ethene Bromine 1,2 - dibromoethene

It is also used as a quantitive test of unsaturation, expressed as the bromine number of a single compound or mixture. The reaction works because the high electron density atthe double bond causes a temporary shift of electrons in the Br-Br bond causing atemporary induced dipole. This makes the Br closest to the double bond slightly positiveand therefore an electrophile.

5) OxidationAlkenes are oxidized with a large number of oxidizing agents . In the presenceof oxygen , alkenes burn with a bright flame to produce carbon dioxide and

water. Catalytic oxidation with oxygen or the reaction with percarboxylic acidsyields epoxides . Reaction with ozone in ozonolysis leads to the breaking of the doublebond, yielding two aldehydes or ketones . Reaction with Concentrated, Hot KMnO 4 (or other oxidizing salts) in an acidic solution will yield ketones or carboxylic acids .

R 1-CH=CH-R 2 + O 3 R 1-CHO + R 2-CHO + H 2O

This reaction can be used to determine the position of a double bondin an unknown alkene.

6) Hydrohalogenation - is the addition of hydrohalic acids such as HCl or HBr toalkenes to yield the corresponding haloalkanes .

CH 3-CH=CH 2 + HBr CH 3-CHBr-CH 2-H
http://en.wikipedia.org/wiki/Electrophilic_halogenationhttp://en.wikipedia.org/wiki/Brominehttp://en.wikipedia.org/wiki/Brominehttp://en.wikipedia.org/wiki/Chlorinehttp://en.wikipedia.org/wiki/Chlorinehttp://en.wikipedia.org/wiki/Vicinal_(chemistry)http://en.wikipedia.org/wiki/Vicinal_(chemistry)http://en.wikipedia.org/wiki/Bromine_numberhttp://en.wikipedia.org/wiki/Organic_oxidationhttp://en.wikipedia.org/wiki/Oxidizing_agenthttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Catalytichttp://en.wikipedia.org/wiki/Percarboxylichttp://en.wikipedia.org/wiki/Epoxidehttp://en.wikipedia.org/wiki/Ozonolysishttp://en.wikipedia.org/wiki/Aldehydehttp://en.wikipedia.org/wiki/Ketonehttp://en.wikipedia.org/wiki/Ketonehttp://en.wikipedia.org/wiki/Carboxylic_acidhttp://en.wikipedia.org/wiki/Hydrohalogenationhttp://en.wikipedia.org/wiki/Hydrohalic_acidhttp://en.wikipedia.org/wiki/Hydrohalic_acidhttp://en.wikipedia.org/wiki/Hydrogen_chloridehttp://en.wikipedia.org/wiki/Hydrogen_bromidehttp://en.wikipedia.org/wiki/Haloalkanehttp://en.wikipedia.org/wiki/Electrophilic_halogenationhttp://en.wikipedia.org/wiki/Brominehttp://en.wikipedia.org/wiki/Chlorinehttp://en.wikipedia.org/wiki/Vicinal_(chemistry)http://en.wikipedia.org/wiki/Bromine_numberhttp://en.wikipedia.org/wiki/Organic_oxidationhttp://en.wikipedia.org/wiki/Oxidizing_agenthttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Catalytichttp://en.wikipedia.org/wiki/Percarboxylichttp://en.wikipedia.org/wiki/Epoxidehttp://en.wikipedia.org/wiki/Ozonolysishttp://en.wikipedia.org/wiki/Aldehydehttp://en.wikipedia.org/wiki/Ketonehttp://en.wikipedia.org/wiki/Ketonehttp://en.wikipedia.org/wiki/Carboxylic_acidhttp://en.wikipedia.org/wiki/Hydrohalogenationhttp://en.wikipedia.org/wiki/Hydrohalic_acidhttp://en.wikipedia.org/wiki/Hydrogen_chloridehttp://en.wikipedia.org/wiki/Hydrogen_bromidehttp://en.wikipedia.org/wiki/Haloalkane


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1- propene Hydrgen 2- Bromo-propaneBromide

Markovnikov's rule

This rule states that in the ionic addition of an unsymmetrical reagent to an

unsymmetrical double bond, the electrophilic agent (usually, though notnecessarily, a proton) will attach itself to the doubly bonded carbon containingthe smaller # of alkyl groups that is, to the one containing the larger # of hydrogens. Thus the Markonikov rule predict the addition of HBr to 1- ethene will giveprimarily 2-Bromoethane. This is, therefore, often referred to as Markonikov addition.If the two carbon atoms at the double bond are linked to a different number of hydrogenatoms, the halogen is found preferentially at the carbon with fewer hydrogensubstituents.

1-ethene 2-Bromoethane

7) PolymerizationA process by which an organic compound reacts with itself to form a high-molecular-weight compound composed of repeating units of the original compound. Thepolymerization of ethene by an ionic, or free-radical, reagent AB is an example.
http://en.wikipedia.org/wiki/Markovnikov's_rulehttp://en.wikipedia.org/wiki/File:AlkeneAndHBrReaction.pnghttp://en.wikipedia.org/wiki/Markovnikov's_rule


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An example of alkene polymerization, in which each Styrene monomer unit'sdouble bond reforms as a single bond with another styrene monomer and formspolystyrene.

8) SynthesisIndustrial methods:The most common industrial synthesis of alkenes is based on cracking of petroleum .

Large alkanes are broken apart at high temperatures, often in the presence of a zeolite catalyst, to give alkenes and smaller alkanes, and the mixture of products isthen separated by fractional distillation. This is mainly used for the manufacture of smallalkenes (up to six carbons).

Zeolites are microporous, aluminosilicate minerals commonly used as commercialadsorbentsNatural zeolites form where volcanic rocks and ash layers reactwith alkaline groundwater. Zeolites also crystallize in post-depositional environmentsover periods ranging from thousands to millions of years in shallow marine basins.Naturally occurring zeolites are rarely pure and are contaminated to varying degrees byother minerals, metals, quartz, or other zeolites. For this reason, naturally occurringzeolites are excluded from many important commercial applications where uniformityand purity are essential.

Related to this is catalytic dehydrogenation , where an alkane loses hydrogen at high

temperatures to produce a corresponding alkene. This is the reverse of the catalytichydrogenation of alkenes.
http://en.wikipedia.org/wiki/Cracking_(chemistry)http://en.wikipedia.org/wiki/Petroleumhttp://en.wikipedia.org/wiki/Zeolitehttp://en.wikipedia.org/wiki/Volcanichttp://en.wikipedia.org/wiki/Volcanic_ashhttp://en.wikipedia.org/wiki/Alkalinehttp://en.wikipedia.org/wiki/Dehydrogenationhttp://en.wikipedia.org/wiki/Dehydrogenationhttp://en.wikipedia.org/wiki/Catalytic_hydrogenationhttp://en.wikipedia.org/wiki/Catalytic_hydrogenationhttp://en.wikipedia.org/wiki/File:ButaneDehydrogenation.pnghttp://en.wikipedia.org/wiki/File:OctaneCracking.pnghttp://en.wikipedia.org/wiki/Cracking_(chemistry)http://en.wikipedia.org/wiki/Petroleumhttp://en.wikipedia.org/wiki/Zeolitehttp://en.wikipedia.org/wiki/Volcanichttp://en.wikipedia.org/wiki/Volcanic_ashhttp://en.wikipedia.org/wiki/Alkalinehttp://en.wikipedia.org/wiki/Dehydrogenationhttp://en.wikipedia.org/wiki/Catalytic_hydrogenationhttp://en.wikipedia.org/wiki/Catalytic_hydrogenation


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9) HYDRATION REACTION

In organic chemistry , a hydration reaction is a chemical reaction in whicha hydroxyl group (OH -) and a hydrogen cation (an acidic proton ) are added to thetwo carbon atoms bonded together in the carbon-carbon double bond which makes upan alkene functional group . The reaction usually runs in a strongacidic, aqueous solution . Hydration differs from hydrolysis in that hydrolysis cleaves thenon-water component in two. Hydration leaves the non-water component intact.

The general chemical equation of the reaction is the following:

RRC=CH 2 in H 2O/acid RRC(-OH)-CH 3

In the first step, the acidic proton bonds to the less substituted carbon of the doublebond following Markovnikov's rule . In the second step an H 2O molecule bonds tothe other, more highly substituted carbon. The oxygen atom at this point has threebonds and carries a positive charge. Another water molecule comes along andtakes up the extra proton.

When carried out in the laboratory, this reaction tends to yield many undesirableside products and in its simple form described here is not considered very useful for the production of alcohol.

Conceptually similar reactions include:

MECHANISM

This is an example reaction mechanism of the hydration of 1-methylcyclohexene to 1-methylcyclohexanol.
http://en.wikipedia.org/wiki/Organic_chemistryhttp://en.wikipedia.org/wiki/Chemical_reactionhttp://en.wikipedia.org/wiki/Hydroxylhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Cationhttp://en.wikipedia.org/wiki/Acidhttp://en.wikipedia.org/wiki/Protonhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Carbon-carbon_double_bondhttp://en.wikipedia.org/wiki/Alkenehttp://en.wikipedia.org/wiki/Functional_grouphttp://en.wikipedia.org/wiki/Aqueoushttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Hydrolysishttp://en.wikipedia.org/wiki/Chemical_equationhttp://en.wikipedia.org/wiki/Markovnikov's_rulehttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/File:Hydrationreaction.pnghttp://en.wikipedia.org/wiki/Organic_chemistryhttp://en.wikipedia.org/wiki/Chemical_reactionhttp://en.wikipedia.org/wiki/Hydroxylhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Cationhttp://en.wikipedia.org/wiki/Acidhttp://en.wikipedia.org/wiki/Protonhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Carbon-carbon_double_bondhttp://en.wikipedia.org/wiki/Alkenehttp://en.wikipedia.org/wiki/Functional_grouphttp://en.wikipedia.org/wiki/Aqueoushttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Hydrolysishttp://en.wikipedia.org/wiki/Chemical_equationhttp://en.wikipedia.org/wiki/Markovnikov's_rulehttp://en.wikipedia.org/wiki/Molecule


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Alkenes are very useful compounds. Major uses are, Lower alkenes are used as fuel and illuminant. These may be obtained by the

cracking of kerosene or petrol. For the manufacture of a wide variety of polymers, e.g., polyethene,

polyvinylchloride (PVC) and teflon etc. As a raw material for the manufacture of industrial Chemicals such as

alcohols, aldehydes, etc. For producing lamp black.

ALKYNESThe alkynes are the third homologous series of organic compounds of hydrogen

and carbon, where there is at least one triple-bond between the atoms in the molecules.H-CC

The alkenes are said to be unsaturated because of the existence of a multiple bond inthe molecule. The general structure of the alkene series of hydrocarbons is C nH2n-2 .The first member of the ethene series is ethyne (previously called acetylene). Thenames of all alkynes end in "-yne". Rules for the systematic naming of alkynes are

similar to those for alkenes. In the case of higher members of the alkene series, thetriple bond may be between the terminal carbon atoms of the chain, or may be betweeninternal carbon atoms in the chain.

Ethyne (Acetylene) HCCHPropyne HCC CH 31-Butyne HCCCH 2CH 31-Pentyne HCC(CH 2)2CH 31-Hexyne HCC(CH 2)3CH 31-Heptyne HCC(CH 2)4CH 31-Octyne HCC(CH 2)5CH 3

1-Nonyne HCC(CH 2)6CH 31-Decyne HCC(CH 2)7CH 3

2-Butyne CH 3CCCH 3


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2-Pentyne CH 3CCCH 2CH 3

The bond formed between the hydrogen atom and the unsaturated carbon atom, andfirst bond between the unsaturated carbon atoms in the ethynes are s bonds (sigma bonds) and these bonds are formed by the end-on overlap of sp hybrid orbitals of thecarbon atoms and the bonds are arranged as far apart in space as possible (i.e. at 180degree) to form a linear molecule. The second and third bonds that makes up the triplebond of the unsaturated carbon atoms in alkenes are p-bonds (pi-bonds), formed by theside-on overlap of the two p-orbitals on each of the carbon atoms. The p-bonds (pi-bonds) are much more reactive than the s bonds (sigma bonds), and react readily inaddition reactions.

Acetylene is a linear molecule, all four atoms lying along a straight line. This linear structure can only be explained by the existence of sp hybridisation of the orbitals of thecarbon atoms of ethyne.

The carbon-carbon triple bond is thus made up of one strong bond and two weaker (bonds; it has a total strength 123 kcal. It is stronger than the carbon-carbon doublebond of ethylene 100 kcal or the single carbon-carbon bond of ethane 83 kcal, andtherefore is shorter than either.

The C-C distance is 1.2 A, as compared with 1.34 in ethylene and 1.54 in ethaneand is a more electronegative grouping than that formed by carbon atoms joined by

either a double or a single bond.The hydrogen attached to the carbon-carbon triple bond in ethyne or in any alkynewhere the carbon-carbon triple bond is situated at the end of a carbon chain is able toseparate from the rest of the molecule as a hydrogen ion; the electronegative carbon isable to retain both electrons from the broken covalent bond.

A significant result of this bonding is that ethyne can unite with metals and so bedistinguished from alkenes by chemical means.

The linear structure does not permit geometric isomerism of ethyne.

ALKYNES CHEMICAL PROPERTIES

1) Combustion of Alkynes

Alkynes are characteristically more unsaturated than alkenes. Thus they add twoequivalents of bromine whereas an alkene adds only one equivalent. Other reactions


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are listed below. Alkynes are usually more reactive than alkenes. They show greater tendency to polymerize or oligomerize than alkenes do. The resulting polymers, calledpolyacetylenes (which do not contain alkyne units) are conjugated and can exhibitsemiconducting properties.

Ethyne burn in air with a luminous, smoky flame, (forming carbon dioxide and water).

2 HCCH + 5 0 2 ==> 4 CO 2 + 2 H 2O

The ethynes are highly dangerously explosives when mixed with air or oxygen.

2) Oxidation of AlkynesEthyne is oxidised by a dilute aqueous solution of potassium permanganate to form

oxalic acid. Thus, if ethyne is bubbled through a solution of potassium permanganatethe solution is decolourised. This is Baeyer's test for unsaturated organic compounds.

KMnO4HCCH ==> HOO = C C = OOHEthyne or

O = COH O = COH

Oxalic Acid

3) Addition Reactions of AlkynesBecause of the unsaturated nature of ethyne addition reactions can occur across thetriple bond.

3.1 Addition of HydrogenWhen acetylene and hydrogen are passed over a nickel catalyst at 150 deg C,(or over platinum black catalyst at room temperature) ethene is first formed andthen this is further reduced to ethane.

NiHCCH + H2 ===> C 2H6

150 C Ethyne Ethane


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When a slight excess of ethyne and ammonia are passed over an alumina catalystat 573 degK, ethanonitrile (i.e. acetonitrile) is produced.

573 C

HCCH + NH3 ==> CH3CN + H2Ethyne Ethanonitrile

5) Polymerization of Alkynes due to Triple BondThe products obtained by polymerising ethyne depend on the conditions used.

When ethyne is passed through a glass tube at 4000 C a little benzene isformed. This is not a suitable way to make benzene in quantity but it is anexample of direct conversion from an open chain to an aromatic compound, (i.e.one with a closed-ring benzenoid structure)

400 C

3HCCH ==> C 6H6Ethyne Benzene

Two molecules of ethyne can be combined to produce vinyl ethyne,HCCCH=CH2, by passing the ethyne into a saturated solution of cuprous

chloride in ammonium chloride continuously in such a way that low conversionsof starting material occur.

Cu 2Cl 2NH4Cl

2HCCH ==> HCCCH = CH2Ethyne Vinyl Ethyne

This linear polymerisation can be extended by altering the conditions of reaction.For example,

HCCCH=CH2 + HCCH ==> CH2=CHCCCH=CH2Vinyl Ethyne Ethyne DiVinyl Ethyne


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6) Substitution Reaction of AlkynesThe reactions of ethynes indicate acidic properties for the hydrogens which areattached to the carbon atoms involved in the triple bond. Ethynes readily formcompounds with metal.

When ethyne is passed through a solution of sodium in liquid ammonia then sodiumacetylide is formed and hydrogen is liberated.

liq.NH3HCCH + 2Na ==> 2HCCNa + H2 Ethyne Sodium Acetylide

The other hydrogen atom in ethyne can be similarly replaced. When ethyne ispassed into a solution of cuprous chloride in ammonia, cuprous acetylide isproduced.

HCCH + Cu 2Cl2 + NH 4OH ==> CuCCCu

Copper Acetylide

Silver acetylide is formed when ethyne is passed into an ammoniacal solution of

silver nitrate.AgNO3NH4OH

HCCH ==> AgCCAg + 2 HNO 3Ethyne Silver Acetylide

These substitution reactions which ethynes undergo to form compounds withmetals does not occur with the alkenes. These reactions can be used as tests to


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distinguish between acetylene and ethylene. When acetylene is passed throughan ammonical solution of silver nitrate or cuprous chloride , at roomtemperature, precipitates of silver acetylide (white) or cuprous acetylide (red)are formed.

In addition to distinguishing ethyne from ethene by chemical means, thesereactions provide a useful method for the preparation of higher alkynes:

HCC-Na + + CH 3I ==> HCCCH 3 + NaIPropyne

Warning: Methyl acetylides are explosive when dry so great care should betaken in their preparation. The metal acetylides can be destroyed when they arestill wet by warming with dilute acid which will regenerate the parent ethyne.

HCC-Na + + HNO3 ==> HCCH + NaNO3

ALKYNES PHYSICAL PROPERTIES

Alkynes are compounds which have low polarity, and have physical properties that areessentially the same as those of the alkanes and alkenes.

1. They are insoluble in water.2. They are quite soluble in the usual organic solvents of low polarity (e.g. ligroin,ether, benzene, carbon tetrachloride, etc.).

3. They are less dense than water.4. Their boiling points show the usual increase with increasing carbon number.5. They are very nearly the same as the boiling points of alkanes or alkenes with

the same carbon skeletons.


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Alkynes Preparation:

The carbon-carbon triple bond of the alkynes is formed in the same way as a doublebond of the alkenes, by the elimination of atoms or groups from two adjacent carbons.

W X W XHC - CH ==> HC = CH ==> HCCH

X XAlkane Alkene Alkyne

The groups that are eliminated and the reagents used are essentially the same as in thepreparations of alkenes.

Alkynes Reactivity:The unsaturated nature of alkynes means that most of their reactions will besimilar to those of alkenes (i.e. electrophilic addition), because of the availabilityof the loosely held pi-electrons. The carbon to carbon triple bond is less reactive thanthe carbon to carbon double bond towards electrophilic reagents. As well as the additionreactions, alkynes undergo reactions that are due to the acidity of a hydrogen atomattached to the triple bonded carbon.

The carbon-carbon triple bond in ethyne is thus made up of one strong sigma-bondand two weaker pi-bonds. It has a total strength 123 kcal/mole. This is stronger than

the carbon-carbon double bond of ethylene which has a total strength of 100 kcal/moleor the single carbon-carbon bond of ethane which has a total strength of 83 kcal/mole.

The carbon-carbon bond lengths, which depend on the strengths of the bonds are: HCCH 1.20 Angstrom Units

Ethyne

H2C=CH 2 1.34 Angstrom Units Ethylene

H3C CH 3 1.54 Angstrom UnitsEthane

The ethynyl radical, CHC* , is a more electronegative group than that formed by carbonatoms joined by either a double or a single bond. Thus, the hydrogen attached to thecarbon-carbon triple bond in ethyne, or in any alkyne where the carbon-carbon triplebond is situated at the end of a carbon chain, is able to separate from the rest of themolecule as a hydrogen ion, so that the alkyne shows acidic properties. The


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electronegative carbon is able to retain both electrons from the broken covalent bond. Asignificant result of this bonding is that ethyne can form compounds with metals and sobe distinguished from alkenes by chemical means.

USES OF ALKYNES: Alkynes are generally used as the starting materials for the manufacture of a

large number of organic compounds of industrial importance such as, chloroprene, vinylchloride etc.CHLOROPRENE~ has the formula CH2=CCl-CH=CH2. This colorless liquid is themonomer for the production of the polymer polychloroprene, a type of synthetic rubber.Polychloroprene is better known to the public as Neoprene, the trade name given byDuPont.VINYL CHLORIDE~ the formula CH2:CHCl. It is also called vinyl chloride monomer,or VCM. This colorless compound is an important industrial chemical chiefly used toproduce the polymer polyvinyl chloride (PVC). At ambient pressure and temperature,vinyl chloride is a gas with a sickly sweet odor. It is highly toxic, flammable andcarcinogenic.

CYCLOALKYNE

Cyclooctyne: the smallest isolable cycloalkyne

In organic chemistry , a cycloalkyne is the cyclic analog of an alkyne . A cycloalkyneconsists of a closed ring of carbon atoms containing one or more triple bonds . Becauseof the linear nature of the C-CC-C alkyne unit, cycloalkynes are usually highly strainedand can only exist when the number of carbon atoms in the ring is great enough toprovide the flexibility necessary to accommodate this geometry . Consequently,cyclooctyne (C 8H12) is the smallest cycloalkyne capable of being isolated and stored asa stable compound. Despite this, smaller cycloalkynes can be produced and trapped bya suitable reagent.
http://en.wikipedia.org/wiki/Organic_chemistryhttp://en.wikipedia.org/wiki/Analog_(chemistry)http://en.wikipedia.org/wiki/Alkynehttp://en.wikipedia.org/wiki/Alkynehttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Molecular_geometryhttp://en.wikipedia.org/wiki/File:Cyclooctyne.svghttp://en.wikipedia.org/wiki/Organic_chemistryhttp://en.wikipedia.org/wiki/Analog_(chemistry)http://en.wikipedia.org/wiki/Alkynehttp://en.wikipedia.org/wiki/Covalent_bondhttp://en.wikipedia.org/wiki/Molecular_geometry


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