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
ammonium cyanate, NH4CNO,
heated gave (organic) urea, (NH2)CO(NH2).
– (Mineral)
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 psychotropic
chemical 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 n4 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:
cis for the same side
and trans for the opposite
cis-2-butene
trans-2-butene
Alkynes, CnH2n–2
propyne
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.
anthracene (edge on)
bromobenzene
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.
isobutraldehyde or
methylpropanal
Functional Groups
Organic backbones can bear heteroatoms 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.
Alcohols, R–OH
The –OH makes alcohol polar enough
to hydrogen bond.  water soluble
 Fermentation product but vulnerable to
oxidation to aldehyde and acid.

yeast
+2
2
glucose, C6H12O6
ethanol
CO2
O
C
H
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.
quinone
benzaldehyde,
“bitter almond”
O
C
O–H
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.


+
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.