Zumdahl’s Chap. 22

Organic Chemistry

Chapter Contents Introduction Alkanes CnH2n+2

– Isomers– Nomenclature

– Cycloalkanes CnH2n

Alkenes CnH2n

Alkynes CnH2n–2

Aromatics Functional Groups

– Alcohols– Aldehydes– Ketones– Carboxylic Acids– Esters– Amines

Organic Chemistry Once upon a time …

– It was believed that organic chemicals could only arise in life processes …

– That they were a product of life’s vitality. In 1828, German chemist Friedrich

Wöhler dispelled that myth when– (Mineral) ammonium cyanate, NH4CNO,

heated gave (organic) urea, (NH2)CO(NH2). As if we needed another source.

Modern Views With the exception of petroleum

products, geological and elemental carbon is inorganic carbon.

Other carbon-containing molecules are organic by virtue of carbon’s presence.

There are no end to the combinatorial possibilities since C bonds to C!

Carbon’s Flexibility sp, sp2, sp3 mean a rich geometry of

180°, 120°, and 109.43° angles in virtually endless chains and branches of organic molecules.

The most potent psychotropicchemical cocktail on Earth …CHOCOLATE!

Carbon’s Reactivity

NOT. With the exception of unsaturated sites

(multiple carbon-carbon bonds), it is at the heteroatoms (non-CH atoms, X) in an organic molecule where lies the reactive site.

Common CX combinations are called functional groups and dictate reactivity.

Inorganic Carbon Elemental carbon

– Graphite– Diamond

– Buckminsterfullerene Carbon oxides and halides Carbonates and carbides Simple cyano- compounds like HCN.

ALKANES Saturated hydrocarbons, CnH2n+2.

– “Saturated” because they can’t take any more hydrogen atoms!

– Straight chains are H3C–(CH2)n–2–CH3

– Gaseous for n<5; solid for n>17 @ STP.– Inert (but for strong oxidizers)– Pathologically nonpolar.– Waxes, oils, & fuel gases as n decreases.

Old Possum’s Naming After n=4, the prefixanes have Greek

numbers as their prefixes.– 5=pent, 6=hex, 7=hept, 8=oct, 9=non,

and 10=dec, 20=eicos, 30=triacos But n4 are named historically

– CH4, Methane (“intoxicate” from the Greek)

– Ethane, Propane, and Butane for 2,3,4.

Branching & Isomers After n=3, it’s possible to let some C’s

bond with more than 2 other carbons.– But fewer than 5, of course!

– The # of structural isomers possible thereby grows exponentially with n.

– These isomers have similar chemical and physical properties.

– So they’re a bit expensive to separate, and one sees bottles labeled merely “hexanes.”

Isomer Naming Older conventions would have that as

“isooctane,” but a good IUPAC name results from the following:– Name the longest C chain (pentane)– List the side groups in alphabetical order

with Greek prefixes (trimethylpentane)– Supply (smallest possible) positional indices

(2,2,4 trimethylpentane)– The gasoline power rating standard molecule.

Cycloalkanes, CnH2n

If the two end C’s lose 1 H each, they have free valence to close a ring; voila, cyclo(whatever)ane.– Again properties similar to straight chains.– Can now have conformational isomers!– E.g., BOAT cyclohexane versus CHAIR

See the C3

and S6 here?

Alkenes, CnH2n

Cycle formation isn’t the only possible result of dehydrogenation.

Adjacent C’s can double bond, C=C, making an (unsaturated) alkene.– Much more reactive (vulnerable e– pair)– Rigid orbitals rigid planar partners!– E.g., trans-5-methyl-2-hexene

Obligatory plane seen edge on

Alkene Isomers While an sp3 CX2Y2 has only 1 isomer,

(every X and Y is adjacent to all the others)

the sp2 alkene C2X2Y2 has cis & trans isomers (where X is or isn’t on the same side of = as X).

– For longer hydrocarbons, cis & trans refer to the side the chain extends:

and trans for the opposite

cis-2-butene trans-2-butene

cis for the same side

Alkynes, CnH2n–2

sp triple bonding makes a rigid 180° segment in a hydrocarbon.

It too is vulnerable to attack across the multiple bond site.– Double & triple bonds can suffer addition

where an AB molecule single bonds A and B to an unsaturated site. H2, HX, and X2 (where X is halogen) are favorites.

propyne

Unsaturated Cycles Earlier we noted the stability lent to

benzene, C6H6, by MOs. Alternating single/double cycles occur

in many organic molecules similarly.– This class is called “aromatic” (by virtue

of their aroma).– The structure is often preserved in their

chemical reactions; they don’t add, they substitute instead.

bromobenzeneanthracene (edge on)

Functional Groups Organic backbones can bear hetero-

atoms as reactive sites. Alkyl root symbolized as R, a generic

hydrocarbon radical (methyl, ethyl, etc.)

Functional groups append R, e.g.,R–OH, an alcohol, or R–CHO, aldehyde.

R–CO2H, a carboxylic acid, R–NH2, amine.

isobutraldehyde ormethylpropanal

Alcohols, R–OH The –OH makes alcohol polar enough

to hydrogen bond. water soluble Fermentation product but vulnerable to

oxidation to aldehyde and acid.

glucose, C6H12O6

yeast

ethanol

2

CO2

+ 2

Aldehydes, R–CHO Next C oxidation state up from alcohol.

– Degradation product in your liver! If C=O isn’t a chain end substituent,

it’s not an aldehyde but a ketone. Aldehydes are often flavorings, but Ketones are industrial solvents.

OC H

benzaldehyde,“bitter almond”

quinone

Carboxylic Acids R–CO2H

Usual highest C ox. state in organics. End product of body’s alcohol degradation.

Weakly acidic but important buffers. React with alcohols to make highly

flavorful esters … a condensation rxn.

OC O–H

+ +

butanoic acid“rancid yak butter”

ethanol ethyl butyrate“pineapple”

water

Amines, Rn–NH3–n

Come in three varieties, n = 1, 2, & 3.– “Primary” amines, n=1, are at chain end.– “Secondary” amine N bonds to 2 carbons.– “Tertiary” amines bond to 3 C.

– Weak base Kb diminishes as n increases.

Alcohols are also primary, secondary, and tertiary. (Primary are on end carbons.)

– But this refers to the bonding of the C to which OH is attached.

Coniine (2ndary) “hemlock”2-propyl-piperidine

Mixed Functionality So H2NCH2CH2OH is an alcohol and

an amine; it becomes ethanolamine. But the monster C9H14N4O3 would be

agony to call by its IUPAC name.– So it’s known by it common name,

carnosine.How many Ka and Kb are expected?

1 and 4, respectively.