Kaplan MCAT OChem Ch. 11: Amines and N-containing compounds

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amine nomenclature

NR3

amine nomenclature

normally have lone pair of electrons

amine nomenclature

classified according to number of alkyl (aryl) group to which bounded (1, 2, 3)

quaternary ammonium compound

N atom attached to 4 alkyl groups has pos charge (bond from lone pair)

amine common name

alkylamine

amine

suffix; -amine
prefix: amino-

N

used to label sub attached to N in 2ndary and 3rd amines

list separate ones for each diff. substituent

aromatic amines

derivates of aniline (C6H5NH2) using common or as derivative of benzeneamine

amides

condensation prod. of carb acid and amines

carbamates

gen. formula = RNHC(O)OR'

carbamates

N attached to carbon, so fall into amide category

carbamates

have O on other side of carbonyl w/ alkyl or aryl group attached to it:

http://upload.wikimedia.org/wikipedia/commons/thumb/4/41/Carbamate-group-2D.png/220px-Carbamate-group-2D.png

carbamates

derived from isocyanates

isocyanates

gen. formula: RNCO

isocyanates

both DB to both oxygen and nitrogen => carbon is polar and can be attacked by Nu:

http://upload.wikimedia.org/wikipedia/commons/2/2b/Isocyanate-group.png

isocyanates

when attacked by alcohol => carbamate

carbamates

urethanes

urethanes

AKA carbamates, and can form polyurethanes

urethanes

useful and versatile polymer

enamines

N analogs of enols, instead of OH, an amine group is attached to C=C (enamines are to N as enols are to O):



http://upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Enamine-2D-skeletal.png/200px-Enamine-2D-skeletal.png

imines

contain N=C:

http://upload.wikimedia.org/wikipedia/commons/e/e9/Imine-2D-skeletal.png

nitriles/cyanides

-C≡N,

prefix: cyano-
suffix: -nitrile

nitro

compounds that contain this group, NO2

az

compound that contains N

diazo

compounds w/ N2 functionality, w/ two Ns at the end of a chain resonating between DB and TB

lose N2 => carbenes

carbenes

highly reactive carbons w/ only 6 valence electrons (usually seen as C w/ two R groups and a lone pair of electrons)

azides

compounds w/ linear N3 functionality (DB between 3 nitrogens)

azides

when loses N2 => nitrenes:

http://upload.wikimedia.org/wikipedia/commons/6/6c/Azide-2D.png

nitrenes

N analogs of carbenes

nitrenes

tend to have 6 valence electrons distributed in one bond to R group and two lone pairs of electrons

AA

are amines

pep bonds between these in proteins are amide bonds

BP of amines

between alkane and alcohols

as MW inc

BP incs

primary and secondary amines

can H bond, not as strong as alcohols

tertiary amines

can't H bond => lower BP

N atom in amine

sp3, three sub to complete and a lone pair => basic and Nu

N atoms

tech chiral due to geo of orbitals

enantiomers can't be isolated because they interconvert rapidly (nitrogen inversion)

nitrogen inversion

inversion of the sp3 orbital occupied by the lone pair

6 kcal/mol => will not be optically active

if at very low temp or if structure prevents inversion of molecule => optically active (ex: quaternary ammonium salts since lack of lone pair)

amines

are bases => readily accept protons => ammonium ions

pKb = 4 (more than ammonia, less than OH)

aromatic amines

like aniline (pKb = 9.42) are far less basic than aliphatic since EW effect reduces bascitiy of amino group

aromatic amines

other groups affect basicity of anilines

EDG => inc. basicity
EWG => red.

amines

WA (pKa = 35), thus SB needed to deprotonate

types of synthesis of amines

Alkylation of ammonia

reduction

types of alkylation of ammonia

direct

gabriel synthesis

types of reduction (amines)

nitro compounds

nitriles

imines

amides

direct (alkylation of ammonia )

alkyl halides + ammonia => alkylammonium halide salts + alkyl halide => more complex products

direct (alkylation of ammonia )

ammonia (Nu) => displaces halide atom (Sn2)

direct (alkylation of ammonia )

salt treated w/ base => alkylamine product

direct (alkylation of ammonia )

often leads to side products: alkylamine as Nu (lone pair and electron donating properties of alkyl group) on N + alkyl halide => complex products

gabriel synthesis

converts a primary alkyl halide to primary amine (sn2, lone pair of ammonia and halide good LG)

gabriel synthesis

first create a disguised form of ammonia (deprotonated phthalimide) to prevent side product formation => phthalimide => displaces halide ion => N-alkylphthalimide => hydrolyzed w/ aq. base => alkylamine

phthalimide

condensation product of phthalic acid and ammonia, good Nu when deprotonated

N-alkylphthalimide

when halide ions displaced => this forms and doesn't react w/ other alkyl halides

reduction of nitro compounds

can reduce this to primary amines

reduction of nitro compounds

most common reagents is Fe and Zn used w/ dilute HCl

reduction of nitro compounds

useful for aromatic compounds because:
1. nitration of aromatic rings is easy
2. this converts deactivating to activating groups

reduction of nitriles

can be this w/ H and a metal catalyst, or w/ LAH => primary amines

reduction of imines (reductive amination)

aldehyde/ketone + ammonia, a primary amine, or a secondary amine => 1, 2, or 3rd amine

reduction of imines (reductive amination)

carbonyl becomes -OH (carbinolamine) => loses water => imine => but when exposed to hydrogen and metal catalyst => reduction to amine

imine

looks like carbonyl => similar polarity and reactivity

reduction of amides

amides can be this w/ LAH => amines

exhaustive methylation/hoffman elimation (reactions)

1. amine w/ excess methyl iodide => quat. ammonium iodide (methyl on N where H used to be)

exhaustive methylation/hoffman elimation (reactions)

2. treatment w/ silver oxide and water => displaces the iodide ion => ammonium hydroxide => WHEN heated => elimination (e2) => alkene and amine

exhaustive methylation/hoffman elimation (reactions)

predominant alkene formed is least sub because of the bulk of quat. ammonium salt LG

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