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, CO 2, 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, CH 4 Ethane, molecular formula C 2 H 6 –Structural formula (indicates connectivity) is CH 3 CH 3

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) NameMolecular formulaStructural formula MethaneCH 4 EthaneC2H6C2H6 CH 3 PropaneC3H8C3H8 CH 3 CH 2 CH 3 n-ButaneC 4 H 10 CH 3 (CH 2 ) 2 CH 3

Straight-chain alkanes (5 C through 10 C) For straight-chain alkanes 5 C through 10 C, use Greek prefix followed by -ane NameMolecular formulaStructural formula n-pentaneC 5 H 12 CH 3 (CH 2 ) 3 CH 3 n-hexaneC 6 H 14 CH 3 (CH 2 ) 4 CH 3 n-heptaneC 7 H 16 CH 3 (CH 2 ) 5 CH 3 n-octaneC 8 H 18 CH 3 (CH 2 ) 6 CH 3 n-nonaneC 9 H 20 CH 3 (CH 2 ) 7 CH 3 n-decaneC 10 H 22 CH 3 (CH 2 ) 8 CH 3

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 CH 3 (CH 3 )CHCH 3

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 (—CH 3 ) –Ethane becomes ethyl as a branch (—CH 2 CH 3 ), 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 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: Carboxylic acid: Ester: Amine: –NH 2

Alcohols Alcohols: R–OH Methanol: CH 3 OH –Starting material in synthesis of chemical products –Racecar fuel –Highly toxic, causes blindness Ethanol: CH 3 CH 2 OH –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 –CH 3 COOH: ethanoic acid (acetic acid is common name) –CH 3 CH 2 CH 2 CH 2 COOH: pentanoic acid

Esters Esters: RCOOR’ Formed by reaction of carboxylic acid and alcohol RCOOH + R’OH  RCOOR’ + H 2 O 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