Zumdahl’s Chap. 22 : Zumdahl’s Chap. 22 Organic Chemistry Chapter Contents : Chapter Contents Introduction
Alkynes CnH2n–2 Aromatics
Amines Organic Chemistry : 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 : 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 : 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 : 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 : Inorganic Carbon Elemental carbon
Carbon oxides and halides
Carbonates and carbides
Simple cyano- compounds like HCN. ALKANES : 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)
Waxes, oils, & fuel gases as n decreases. Old Possum’s Naming : 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 : 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 : 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 : 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 Alkenes, CnH2n : 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 Alkene Isomers : 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: Alkynes, CnH2n–2 : 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. Unsaturated Cycles : 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. Functional Groups : 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. Alcohols, R–OH : Alcohols, R–OH The –OH makes alcohol polar enough to hydrogen bond. ? water soluble
Fermentation product but vulnerable to oxidation to aldehyde and acid. Aldehydes, R–CHO : 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. Carboxylic Acids R–CO2H : 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. + ? + Amines, Rn–NH3–n : 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. Mixed Functionality : 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.