organic chemistry chapter 22. organic chemistry the study of carbon-containing compounds and their...
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Organic Chemistry
Chapter 22
Organic Chemistry
The study of carbon-containing compounds and their properties.
The vast majority of organic compounds contain chains or rings of carbon atoms.
Organic & Inorganic Compounds
Originally the distinction between inorganic and organic substances was based on whether or not they were produced by living systems.
In 1828, German chemist Friedrich Wohler prepared urea from the inorganic salt ammonium cyanate by simple heating:
heat
NH4OCN ---> NH2CONH2
Hydrocarbons
. . . compounds composed of carbon and hydrogen.
Saturated: carbon-carbon bonds are all single - alkanes [CnH2n+2]
H C
H
H
C
H
H
H
Hydrocarbons(continued)
Unsaturated: contains carbon-carbon multiple bonds.
H C
H
H
C
H
CH
H
Hydrogen Addition
C2H4(g) + H2(g) ---> C2H6(g)
unsaturated saturated
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C
sp3
sp3sp3
sp3
H1s
H1s
H1s
H1s
The carbon-hydrogen bonds in methane.
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C
H
H
C
H
H
H H
(a) (b)
The Lewis structure, space-filling, and ball-and-stick models for ethane.
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(a) (b)
The structures of propane and butane with 109.5o
bond angles.
Structural Isomerism
-- isomers contain the same atoms but one or more different bonds.
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(a)
(b)
Normal butane (n-butane) and the branched isomer, isobutane.
Isomers of Pentane
What are the three isomers of pentane?
1) n-pentane -- straight-chain
2) isopentane -- one branch from 2nd carbon
3) neopentane -- two branches from central carbon
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CH3 CH2 CH2 CH2 CH3
n-Pentane
The straight-chain isomer, n-pentane.
Rules for Naming Alkanes
1. For alkanes beyond butane, add -ane to the Greek root for the number of carbons.
C-C-C-C-C-C = hexane
2. Alkyl substituents: drop the -ane and add -yl.
-C2H5 is ethyl
Rules for Naming Alkanes3. Positions of substituent groups are specified
by numbering the longest chain sequentially. C
C-C-C-C-C-C
3-methylhexane
4. Location and name are followed by root alkane name. Substituents in alphabetical order and use di-, tri-, etc.
See Sample Exercise 22.2 on pages 1062-1064.
Combustion Reactions of Alkanes
C3H8(g) + 5O2(g) ----> 3CO2(g) + 4HOH(g)
2C4H10(g) + 13 O2(g) ----> 8CO2(g) + 10HOH(g)
Substitution Reactions for Alkanes
Primarily where halogen atoms replace hydrogen atoms.
CHCl Cl CCl HClh3 2 4
Dehydrogenation Reactions
Cr2O3
CH3CH3 ----> CH2=CH2 + H2
500oC
ethane ethylene
Cyclic AlkanesCarbon atoms can form rings containing only carbon-carbon single bonds.
C3H6, C4H8, C6H12
Shorthand notation for the cyclic alkanes.
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C C
C
109.5
60
No "head-on"overlap of atomic orbitals
(b)(a)
The molecular structure of cyclopropane andthe overlap of the sp3 orbitals that form the C-C bonds.
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Boat
(b)
These two Hatoms repeleach other
Chair
(a)
The chair and boat forms of cyclohexane.
Alkenes and Alkynes
Alkenes: hydrocarbons that contain a carbon-carbon double bond. [CnH2n]
CC=C propene
Alkynes: hydrocarbons containing a carbon-carbon triple bond. [CnH2n-2]
CCCCC 2-pentyne
Nomenclature for Alkenes
1. Root hydrocarbon name ends in -ene
C2H4 is ethene
2. With more than 3 carbons, double bond is indicated by the lowest numbered carbon atom in the bond.
C=CCC is 1-butene
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H1s
sp2
sp2
sp2
sp2
H1s
2p
C C
sp2
sp2
The bonding in ethylene.
The two stereoisomers of 2-butene. a) cis-2-butene b) trans-2-butene
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H
H
H H
H
H
CC
The bonding in ethane allows rotation and nocis-trans isomerism.
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2p
2pH1s
H
sp
2p
2p
C
sp 2p
2p
2p
C H
H1s
2p
sp
The bonding in acetylene.
Addition Reactions
. . . in which (weaker) bonds are broken and new (stronger) bonds are formed to atoms being added.
CH CHCH H CH CH CHcatalyst2 3 2 3 2 3
propene propane
Halogenation
CH2=CHCH2CH2CH3 + Br2 --->
CH2BrCHBrCH2CH2CH3
1-pentene 1,2-dibromopentane
Aromatic Hydrocarbons
A special class of cyclic unsaturated hydrocarbons.
+ Cl2
FeCl3
Cl
+ HCl
benzene Chlorobenzene
Aromatic Hydrocarbons
phenyl group
Ortho (o-) -- two adjacent substituents.
meta (m-) -- two substituents with one carbon between them.
para (p-) -- two substituents opposite each other.
Refinery Processes
Cracking: large molecules broken down to smaller ones by breaking carbon-carbon bonds.
Pyrolysis (thermal cracking): The process that produces cracking at high temperatures.
Catalytic Cracking: Cracking at lower temperatures.
Catalytic reforming: Alkanes and cycloalkanes converted to aromatic compounds.
The Common Functional Groups
Class General Formula
Halohydrocarbons RX
Alcohols ROH
Ethers ROR
Aldehydes
CRO
H
The Common Functional Groups
Class General Formula
Ketones
Carboxylic Acids
Esters
Amines RNH2
Amides R-C=ONH2
CRO
R'
CRO
OH
CRO
O R'
22_05TTable 22.5 The Common Functional Groups
Functional GeneralClass Group Formula* Example
Halohydrocarbons X (F,Cl,Br,I) R X CH3IIodomethane
(methyl iodide)
Alcohols OH R OH CH3OHMethanol
(methyl alcohol)
Ethers O R O R' CH3OCH3Dimethyl ether
CH2OAldehydes Methanal
(formaldehyde)
CH3COCH3Ketones Propanone
(dimethyl ketoneor acetone)
CH3COOHCarboxylic acids Ethanoic acid
(acetic acid)
CH3COOCH2CH3Ethyl acetateEsters
Amines CH3NH2Aminomethane (methylamine)
C H R C H
O O
C R C R'
O O
C OH R C OH
O O
C O R C O R'
O O
NH2 R NH2
*R and R' represent hydrocarbon fragments.
Alcohols
contain the hydroxyl group (-OH).
Aldehydes & Ketones
contain the carbonyl group ( C=O ).
In ketones the carbonyl group is bonded to two carbon atoms -- CH3C=OCH3.
In aldehydes the carbonyl group is bonded to at least one hydrogen atom -- HCHO.
Carboxylic Acids & Esters
Carboxylic acids contain the carboxyl group
O (-C-OH).
OEsters contain the -C-O- group.
Amines & Ethers
Amines contain -NH2 group.
If one hydrogen is removed and replaced with a hydrocarbon group, it is a primary amine.
If two hydrogen are replaced, it is a secondary amine.
If all three hydrogens are replaced, it is a tertiary amine.
Ethers contain the -O- group.
Polymers
. . . are large, usually chainlike molecules that are built from small molecules called monomers.
Monomer PolymerEthylene PolyethyleneVinyl chloride Polyvinyl
chlorideTetrafluoroethylene Teflon
Types of Polymerization
Addition Polymerization: monomers “add together” to form the polymer, with no other products. (Teflon)
Condensation Polymerization: A small molecule, such as water, is formed for each extension of the polymer chain. (Nylon)