Alkanes and Cycloalkanes

Structure FormsC3H8

Kekul or Wedge/dash

H3C CH2 CH3skeletal

H H

H

H

H

CH3CH2CH3condensed

H H H

2

Classes of HydrocarbonsOrganic Compounds

hydrocarbons (C,H)

heteroatomic (O, N, P, S, X, etc.)

aliphatic (fatty)

aromatic (pleasant smelling)

alkane C C

alkene C C

alkyne C C

cyclic

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Functional Groups

A functional group is an atom or group of atoms that have a characteristic chemical behavior. The chemistry of every organic molecule, regardless of size and complexity, is determined by the functional groups it contains.

4

Functional Groups

O C H3 C O O C O5

H

Types of Functional Groups: Multiple CarbonCarbon Bonds

Alkenes have a C-C double bond Alkynes have a C-C triple bond Arenes have special bonds that are represented as alternating single and double C-C bonds in a sixmembered ring6

Functional Groups

Alkyl halideH H C H H C H H C H H C H Br

R-X where X is any halogen X7

Functional Groups

AlcoholsH H C H H C H H C H H C H OH

R-OH where R is any alkyl group8

Functional Groups

EthersH H C H H C H H O C H H

R-O-R where R is any alkyl group9

Functional Groups

Aldehydes

H O H C H10

C H

Functional Groups

Ketone

H O H H C C C H

H H Propanone (acetone)11

Functional Groups

Carboxylic acids

H O H C HEthanoic acid (acetic acid)12

C OH

Functional Groups

Ester

H H C H

O C O CH3

Methyl ethanoate (methyl acetate)13

Functional Groups

Amine

H H C HMethylamine

NH2

14

Functional Groups

Amide

O H3 C C NH2Ethanamide (acetamide)15

Functional Groups

Acid anhydride

O H3 C

O CH3

C O C

Ethanoic anhydride16

Functional Groups

Acid halide

O H3 C C ClEthanoyl chloride17

Functional Groups

Nitro

O H3 C N O18

Nitromethane

Functional Groups

Arene

benzene19

Functional Groups

Halide

H3 C

Cl

Chloromethane20

Functional Groups

Nitrile

H3 C

C N

Ethanenitrile

21

Functional Groups

Sulfide

H3 C

S

CH3

22

Functional Groups

Thiol

H3 C

S

H

Methanethiol

23

Functional GroupsO OCH3 O N H HO O24

NH2

Alkanes and Alkane Isomers

Alkanes: Compounds with C-C single bonds and C-H bonds only (no functional groups) Connecting carbons can lead to large or small molecules The formula for an alkane with no rings in it must be CnH2n+2 where the number of Cs is n Alkanes are saturated with hydrogen (no more can be added They are also called aliphatic compounds

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AlkanesH3C CH2 CH2 CH3 H H H H H C C C C H H H H H CH3CH2CH2CH3 H C H H C H H CH3(CH2)2CH3

H H C H

H C H

CH3CH(CH3)CH2CH326

Structure

Shape

tetrahedral about carbon all bond angles are approximately 109.5

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Alkane Isomers

CH4 = methane, C2H6 = ethane, C3H8= propane The molecular formula of an alkane with more than three carbons can give more than one structure C4 (butane) = butane and isobutane C5 (pentane) = pentane, 2-methylbutane, and 2,2dimethylpropane Alkanes with Cs connected to no more than 2 other Cs are straight-chain or normal alkanes Alkanes with one or more Cs connected to 3 or 4 Cs are branched-chain alkanes

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Alkanes

straight chain or normal alkanesH H H H C C H H H H H H H C C C H H H H H H H H H C C C C H H H H H

H C H H

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Alkanes

branched chains

H H H H H H H H C C C C C H H H H H H H C H H H H H C C C C H H H H H H C H H H H C C C H H H H C H H30

Branching vs. No Branching

There are 2 isomeric butanes

n-butane

H H C H

H C H

H C H

H C H H

C4H10

n means normal or in a straight chainH H H H C H C C H H H C H H31

isobutane

C4H10

Find the Isomers of C5H12

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Find the Isomers of C6H14Draw the structures for C6H14 starting with the longest chain (6 in a row) H H H H H HH C H C H C H C H C H C H H

next draw all structures with 5 carbons in the longest chain (substitute for the H s)then substitute for other H sH H C H H H H C C C H H H H C H H C H H33

Find the Isomers of C6H14

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Find the Isomers of C7H16

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Isomers

Same chemical formula, but different structure.

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Constitutional Isomers

Isomers that differ in how their atoms are arranged in chains are called constitutional isomers Compounds other than alkanes can be constitutional isomers of one another They must have the same molecular formula to be isomers

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Constitutional IsomerismMolecular Cons titutional Formula Isomers CH 4 C 5 H12 C 10 H22 C 15 H32 C 30 H62 1 3 75 4,347 4,111,846,76338

World population is about 6,000,000,000

Names of Small HydrocarbonsNo. of Carbons 1 2 3 4 5 6 7 8 9 10 Formula Name Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane (CnH2n+2) CH4 C 2H 6 C 3H 8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H2239

Alkyl Groups

Alkyl group remove one H from an alkane (a part of a structure) General abbreviation R (for Radical, an incomplete species or the rest of the molecule) Name: replace -ane ending of alkane with -yl ending

CH3 is methyl (from methane) CH2CH3 is ethyl from ethane

See Table 3.4 for a list

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Types of Alkyl groups

Classified by the connection site (See Figure 3.3) a carbon with one carbon attached to it (primary alkyl group) a carbon with two carbons attached to it (secondary alkyl group) a carbon with three carbons attached to it (tertiary alkyl group) a carbon with four carbons attached to it (quaternary alkyl group)

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Types of Alkyl groups

Classified by the connection site (See Figure 3.3)

a carbon with one carbon attached to it (primary alkyl group) a carbon with two carbons attached to it (secondary alkyl group) a carbon with three carbons attached to it (tertiary alkyl group) a carbon with four carbons attached to it (quaternary alkyl group)

CH3

CH3 CH3 CH3 C CH2CH C CH3 CH3 CH3

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Degree of Substitution

CH31 3

2

4 CH 3

CH3CHCHCH2CH2C CH3 CH2 CH3 CH343

Nomenclature

International Union of Pure and Applied Chemistry

colloquially: eye-you-pac

Devised following WWII ca. 1946-1950

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Naming Alkanes

Compounds are given systematic names by a process that uses

Prefix-Parent-Suffix Named as longest possible chain Carbons in that chain are numbered in sequence substituents are numbered at their point of attachment Compound name is one word (German style) Complex substituents are named as compounds would be

Follows specific rules

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Nomenclature Where are substituents? Prefix-Parent-Suffix

How many carbons? What family?International Union of Pure and Applied Chemistry (IUPAC)46

Nomenclature Prefix-Parent-Suffix

CH3 CH2 CH CH2 CH2 CH CH2 CH3 CH33-ethyl-6-methyl

CH2 CH3

octane47

NomenclatureName Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane Undecane Dodecane

Alkanes have the general formula CnH2n+2

Condensed Structure CH4 CH3CH3 CH3CH2CH3 CH3(CH2)2CH3 CH3(CH2)3CH3 CH3(CH2)4CH3 CH3(CH2)5CH3 CH3(CH2)6CH3 CH3(CH2)7CH3 CH3(CH2)8CH3 CH3(CH2)9CH3 CH3(CH2)10CH3

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The Longest Continuous Chain of Carbon AtomsC-C C -C -C -C -C -C -C -C -C Call possibilites must be examined it wont always be the horizontal one as shown here

9

try these also ..

C -C C- C-C-C -C-C-C-C-C C C

C -C C-C-C- C-C-C-C-C-C

6

8

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Nomenclature

Parent name of the longest carbon chain is alkane Groups attached to the parent chain are called substituents Each substituent is given a name and a number

If substituent occurs more than once, di-, tri-, tetra-, etc.

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Nomenclature

Number the chain to give the substituent encountered first the lowest number If there are different substituents, list them in alphabetical order. The following are not included in alphabetization.

di-, tri-, tetra-, etc. hyphenated prefixes, such as sec- and tert-

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Nomenclature

Alkyl groups

Propyl Isopropyl Butyl Isobutyl sec-butyl tert-butyl

-CH2CH2CH3 -CHCH(CH3)2 -CH2CH2CH2CH3 -CH2CHCH(CH3)2 -CH(CH3)CH2CH3 -C(CH3)3

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Nomenclature

Alkyl groupsName pentyl isopentyl Condens ed Structural Formula -CH 2 CH2 CH 2 CH 2 CH 3 -CH 2 CH2 CHCH3 CH 3 CH3 neopentyl -CH 2 CCH 3 CH353

Nomenclature

Find the longest chain.

CH 2 CH 3 CH3CH2CH2CH CH3CH3 CH2 H3C CH CH CH2CH 3 CH2CH 2CH3

hexane

heptane

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Nomenclature

If two different chains of equal length are present, choose the one with the larger number of branch points.

CH3 CH3CHCHCH2CH2CH3 CH2 CH355

Nomenclature

Number the atoms in the main chain:

Begin at the end nearer the first branch point (lower number).1 2

CH3 CH23 4

H 3C

CH CH CH2 CH3 CH2 CH2 CH35 6 756

Nomenclature

If branching is equal distant away from both ends of the parent chain, begin at the end nearer the second branch point.

H3C CH2 CH3 CH3CHCH 2CH2CHCHCH2CH3 CH2 CH357

Nomenclature

Identify the number of substituents:

Assign a number to each substituent according to its point of attachment to the main chain.

3-ethyl 9 8 4-methyl H3C CH2 CH3 3 7-methyl CH3CHCH2CH2CHCHCH2CH3 7 6 5 4 CH2 CH3 2 1

3-ethyl-4,7-dimethylnonane

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Nomenclature

If there are two substituents on the same carbon, assign them both the same number.

4-ethyl-2,4-dimethylhexane

CH3 CH3 CH3CH2CCH2CHCH3 CH2 CH3

2-methyl 4-methyl 4-ethyl

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Nomenclature

Write the name as a single word, using hyphens to separate the different prefixes and commas, to separate numbers. Use di-, tri-, etc. if more than one identical substituents Dont use these prefixes for alphabetizing purposes.

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Nomenclature3-methylhexane

CH2 CH3 CH3CH2CH2CH CH361

Nomenclature4-ethyl-3-methylheptane

1 CH33 CH 2 CH2 CH 2 4 CH3CHCHCH2CH3 CH 33 CHCHCH 2CH 3 CH2 CH2 CH3 CH 2 CH2 CH 3 6 7 5

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Nomenclature3-ethyl-2-methylhexane

CH3 CH3CHCHCH2CH2CH3 CH2 CH363

Nomenclature

Name a complex substituent and begin numbering at the point of attachment and set it off in parentheses.

CH3 CH3CH CHCH2CH2CH CH2CH CH3 CH3 CH3 CH2CH2CH2CH364

Nomenclature2,3-dimethyl-6-(2-methylpropyl)decane 2-methylpropyl CH3 1CH3CH CHCH2CH2CH CH2CH CH3 CH3 CH3 CH2CH2CH2CH365

2

3

CH 3 CH 3

Nomenclature

CH CHCH 3

1,2-dimethylpropyl

CH 3 CH3 CH 3CH 2CH2CH2CH CH CHCH3 CH 2 CH 3 CH 2 CH CH 3

2-methyl-5-(1,2-dimethylpropyl)nonane66

Nomenclature-Historical

Threecarbon alkyl group:

CHCH3

isopropyl (i-pr)

CH367

Nomenclature-Historical

Fourcarbon groups:

CHCH2CH3 CH3

CH2CHCH3 CH3

CH3 C CH3 CH3

sec-butyl

isobutyl

tert-butyl

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Nomenclature-Historical

Fivecarbon alkyl groups:

CH2CH2CHCH3 CH3isopentyl

CH3 CH2CCH3 CH3neopentyl69

Nomenclature

H 3C CH CH3 H3C CH2 CH 2 CH CH2 CH2CH 34-(1-methylethyl)heptane or 4-isopropylheptane

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If you can name this, you can name anything!CH31 2 3 4 5 6

CH3 CH3

CH3 CH CH2 CH CH2 C CH3 CH 7 CH3 89

CH2 CH2 CH371

4-isopropyl-2,6,6-trimethylnonane

How about this?CH3

CH3CH22-cyclobutyl-5-methylhexane not (1,4-dimethylpentyl)cyclobutane

CH3

CH3

5-ethyl-1,1,3-trimethyl-2-(2methylpentyl)cyclohexane72

Properties of Alkanes

Called paraffins (low affinity compounds) because they do not react as most chemicals They will burn in a flame, producing carbon dioxide, water, and heat They react with Cl2 in the presence of light to replace Hs with Cls (not controlled)

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Physical Properties

Boiling points and melting points increase as size of alkane increases Forces between molecules (temporary dipoles, dispersion) are weak

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Alkane MP & BP Trends

The dependence of the boiling and melting points on chain length can be explained in terms of increasing attractive van der Waals interactions as the chain length increases.

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Cycloalkanes

Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes rings of CH2 units, (CH2)n, or CnH2n Structure is shown as a regular polygon with the number of vertices equal to the number of Cs (a projection of the actual structure)

cyclobutane cyclopropane cyclopentane cyclohexane76

Cycloalkanes

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CycloalkanesCH2OH CO H3C OH H O Hcortisone78

O H3C

Cycloalkanes

Structure and nomenclature

to name, prefix the name of the corresponding openchain alkane with cyclo-, and name each substituent on the ring if only one substituent, no need to give it a number if two or more substituents, number from the substituent of lowest alphabetical order where there is choice, number to give substituents the lowest set of numbers

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Naming Cycloalkanes

Count the number of carbon atoms in the ring and the number in the largest substituent chain. If the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted cycloalkane For an alkyl- or halo-substituted cycloalkane, start at a point of attachment as C1 and number the substituents on the ring so that the second substituent has as low a number as possible. Number the substituents and write the name

if only one substituent, no need to give it a number

See text for more details and examples

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Nomenclature

For alkyl-substituted cycloalkanes, start at the point of attachment and number the substituents on the ring so as to arrive at the lowest sum.CH 31 6 5 4 2 3

1,3-dimethylcyclohexane not 1,5-dimethylcyclohexaneCH 381

Nomenclature

Halogens are treated exactly like alkyl groups.1-bromo-3-ethyl-5-methylcyclohexane Br CH33 4 2 1

Br

CH3CH2

CH 382

1-bromo-2-methylcyclobutane

Cis-Trans Isomerism in Cycloalkanes

Rotation about C-C bonds in cycloalkanes is limited by the ring structure Rings have two faces and substituents are labeled as to their relative facial positions There are two different 1,2-dimethyl-cyclopropane isomers, one with the two methyls on the same side (cis) of the ring and one with the methyls on opposite sides (trans)

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Stereoisomers

Compounds with atoms connected in the same order but which differ in three-dimensional orientation, are stereoisomers The terms cis and trans should be used to specify stereoisomeric ring structures Recall that constitutional isomers have atoms connected in different order

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Cis-Trans IsomerismH3 C CH3

H3 C CH3

cis-1,2-dimethylcyclopropane trans-1,2- dimethylcyclopropane

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Cis-trans isomerism

1,2-dimethylcyclopentane

H H H

H H H

H

H H H

H

H CH3 H

H CH3 CH3 cis-1,2-dimethylcyclopentane

H

CH3 H trans-1,2-dimethylcyclopentane

86

Cis-trans isomerism

1,4-Dimethylcyclohexane

planar hexagon representationsH CH3 H H

H H3 C trans -1,4-Dimethylcyclohexane

H3 C CH3 cis -1,4-Dimethylcyclohexane

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