Chapter 19: Organic chemistry

Chemistry 1020: Interpretive chemistry

Andy Aspaas, Instructor

Organic compounds

• Organic compounds: carbon containing compounds

– Specifically, with carbon-carbon covalent bonds

– Carbonates, CO2, CO are not organic

• VSEPR theory: carbon has 4 electron pairs

– A tetrahedral electron pair arrangement– 4 covalent bonds, no lone pairs– Tetrahedral molecular shape as well

Hydrocarbons and alkanes

• Hydrocarbons contain only carbon and hydrogen

• Alkanes are hydrocarbons with only single bonds (no double or triple bonds)

– Saturated: only single bonds

• Simplest alkane: methane, CH4

• Ethane, molecular formula C2H6

– Structural formula (indicates connectivity) is CH3CH3

• Straight-chain (or “normal”) alkanes have carbons all attached in a row

• n- at beginning indicates straight-chain (normal)

Straight-chain alkanes (1 C through 4 C)

Name Molecular formula Structural formulaMethane CH4 CH4

Ethane C2H6 CH3CH3

Propane C3H8 CH3CH2CH3

n-Butane C4H10 CH3(CH2)2CH3

Straight-chain alkanes (5 C through 10 C)

• For straight-chain alkanes 5 C through 10 C, use Greek prefix followed by -ane

Name Molecular formula Structural formula

n-pentane C5H12 CH3(CH2)3CH3

n-hexane C6H14 CH3(CH2)4CH3

n-heptane C7H16 CH3(CH2)5CH3

n-octane C8H18 CH3(CH2)6CH3

n-nonane C9H20 CH3(CH2)7CH3

n-decane C10H22 CH3(CH2)8CH3

Isomerism in alkanes

• n-Butane has an isomer (same number and kind atoms, different bonds)

– Same molecular formula, different structural formula

• Isobutane: branched, all carbons not in a row

• CH3(CH3)CHCH3C CH3H3C

CH3

H

Isomerism in alkanes

• Iso- prefix means branched once

• Neo- prefix means branched twice

– n-Pentane, isopentane, neopentane

• More complex branched alkanes require different naming rules

– Any of the straight-chain alkanes can be made into “substitutents” - or branches off a main chain

– Methane becomes methyl as a branch (—CH3)

– Ethane becomes ethyl as a branch (—CH2CH3), etc

Naming complex branched alkanes

• Start by identifying the longest carbon chain

• Identify branches off the longest chain as their substituent name (methyl, ethyl, propyl, etc)

• Number longest chain starting at end closest to the first branch

• Name the compound, starting with branches and indicating the number on the main chain to which the branch is attached

Naming branched alkanes

H3C CH2

CH2

CH

H2CHC

CH2

CH

CH3

CH2CH3

H3C

H3C

• First identify longest chain (9 carbons)

• Number chain starting at end closest to a branch

• Identify branches by first numbering them (from main chain number)

– 2-methyl, 4-ethyl, 6-methyl

• Combine identical branches by saying 2,6-dimethyl

• Then give chain name• 4-ethyl, 2,6-dimethyl nonane

Alkenes and alkynes

• Alkenes: hydrocarbons with carbon-carbon double bonds

• Alkynes: hydrocarbons with carbon-carbon triple bonds

• Name by first finding longest carbon chain• Chain name is same as alkane, but end is -ene for

double bond, -yne for triple bond• Start numbering on end closest to double/triple bond• Location of multiple bond is given by the smaller

numbered carbon involved in the bond

Functional groups

• Most organic molecules are simply hydrocarbons with different groups of atoms attached

– Functional groups: common groups of atoms found in organic molecules

Common functional groups

• Alkyl halide: –X (where X is F, Cl, Br, or I)

• Alcohol: –OH

• Ether: –O–

• Aldehyde:

• Ketone: C

O

• Carboxylic acid:

• Ester:

• Amine: –NH2

C

O

OH

C

O

OH

C

O

O

C

O

H

Alcohols

• Alcohols: R–OH• Methanol: CH3OH

– Starting material in synthesis of chemical products

– Racecar fuel– Highly toxic, causes blindness

• Ethanol: CH3CH2OH– Formed by fermentation of glucose– Important gasoline additive

Carboxylic acids

• Carboxylic acid: R–COOH

• Name by dropping –e from parent hydrocarbon name, and adding –oic acid

– CH3COOH: ethanoic acid (acetic acid is common name)

– CH3CH2CH2CH2COOH: pentanoic acid

R C

O

OH

Esters

• Esters: RCOOR’

• Formed by reaction of carboxylic acid and alcohol

• RCOOH + R’OH RCOOR’ + H2O

• Name by first using alcohol fragment as a fragment name

– Then add root of carboxylic acid followed by –ate

• Ex. Acetic acid + ethyl alcohol ethyl acetate

R C

O

O R'