organic chemistry II exam II

Compounds that have only carbon and hydrogen atoms bonded to the carbonyl.

Aldehyde and keton

name the compound

aldehyde

name the compound

ketone

name the compound

carboxylic acid

name the compound

acid chloride

name the compound

ester

name the compound

amide

An electrostatic potential map shows the

electron-deficient carbon and the electron rich oxygen atom of the carbonyl group

The Carbonyl carbons are

sp2 hybridized, trigonal planar, and have bond angles that are ~120 degrees.

the carbonyl group resembles the

trigonal planar sp2 hybridized carbons of a C=C

The electronegative oxygen atom in the carbonyl group (C=O) means that the bond is

polarized,

The electronegative oxygen atom in the carbonyl group (C=O) means that the bond is polarized, making the carbonyl carbon

electron deficient

the carbonyl group with an oxygen atom is represented by two resonance structures

Carbonyl carbons are electrophilic and react with

nucleophiles

product of addition

product of substitution

mechanism that is called nucleophilic addition

Aldehydes and ketones react with nucleophiles to form addition products by a two-step process: nucleophilic attack followed by protonation

Aldehydes are more reactive than

ketones towards nucleophilic attack for both steric and electronic reasons

Carbonyl compounds with leaving groups react with nucleophiles to form

substitution products

which group has the ost leaving ability

CL with or and oh folowing behind it

Carbonyl compounds can be either

reactants or products in oxidation–reduction reactions.

product

product

product

The most useful reagents for reducing aldehydes and ketones are

the metal hydride reagents

Treating an aldehyde or ketone with NaBH4 or LiAlH4 , followed by H2O or some other proton source affords an

alcohol

product

product

Catalytic hydrogenation also reduces aldehydes and ketones to

1° and 2° alcohols, respectively, using H2 and a catalyst

product

product

When a compound contains both a carbonyl group and a carbon–carbon double bond, selective reduction of one functional group can be achieved by

proper choice of the reagent

A C=C is reduced faster than a C=O with

H2 (Pd—C)

A C=O is readily reduced with____________, but a C=C is iner

NaBH4 and LiAlH4

2-cyclohexenone, which contains both a C=C and a C=O, can be reduced to

three different compounds depending upon the reagent used

reacts with nabh4 ch3oh

h2(1 equiv) pd-c

h2 (excess) pd-c

When an achiral reagent is used, a

racemic product is obtained in which case both enantiomers are formed in equal amounts

reminder that this is acrhiral due to there being no carbon that has 4 unique connections

Since the carbonyl is planar, the hydride can approach the double bond with

equal probability from both sides.

A reduction that forms one enantiomer predominantly or exclusively is an

enantioselective or asymmetric reduction

An example of chiral reducing agents are the

enantiomeric CBS reagents

CBS refers to

Corey, Bakshi, and Shibata

The (S)-CBS reagent delivers (H:− ) from the front side of the C=O. This generally affords the .

R alcohol as the major product

The (R)-CBS reagent delivers (H:− ) from the back side of the C=O. This generally affords the

S alcohol as the major product.

s cbs reagent

r cbs reagent

Diisobutylaluminum hydride [(CH3 )2CHCH2 ]2AlH, abbreviated DIBAL-H, has two bulky isobutyl groups which makes this reagent

less reactive than LiAlH4 .

Lithium tri-tert-butoxyaluminum hydride, LiAlH[OC(CH3 )3 ]3 , has three electronegative O atoms bonded to aluminum, which makes this reagent

less nucleophilic than LiAlH4 .

Acid chlorides and esters can be reduced to

either aldehydes or 1° alcohols depending on the reagent

liaih4/h2o

liaih[oc(ch3)3]3/h20

In the reduction of an acid chloride, Cl− comes off as

the leaving grou

In the reduction of the ester, CH3O− comes off as the leaving group, which is then protonated by H2O to form

CH3OH

liaih4/h20

dibal-h/h20

Carboxylic acids are reduced to 1° alcohols with

LiAlH

LiAlH4 is too strong of a reducing agent to stop the reaction at the

aldehyde stage.

Since −NH2 is a very poor leaving group, it is

never lost during the reduction, and therefore an amine is formed.

Unlike the LiAlH4 reduction of all other carboxylic acid derivatives, which affords 1° alcohols, the LiAlH4 reduction of amides forms

amines

Aldehydes can also be oxidized selectively in the presence of other functional groups using

silver(I) oxide in aqueous ammonium hydroxide

Since ketones have no H on the carbonyl carbon,

they do not undergo the oxidation reaction using silver oxide

the most common organometallic metals

all of the above

Other metals found in organometallic reagents are

Sn, Si, Tl, Al, Ti, and Hg

Organolithium (RLi) and organomagnesium (RMgX) reagents contain very polar carbon-metal bonds and are therefore

very reactive reagents

Organomagnesium reagents are called

Grignard reagents

Organocopper reagents (R2CuLi), also called organocuprates, have a less polar carbon–metal bond and are therefore

less reactive.

Organolithium and Grignard reagents are typically prepared by reaction of an

alkyl halide with the corresponding metal

Grignard reagents are usually prepared in

diethyl ether (CH3 CH2 OCH2 CH3 ) as solvent.

Organocuprates are prepared from organolithium reagents by reaction with a

Cu+ salt, often CuI

Acetylide ions are another example of

“organometallic reagents”

Since sodium is even more electropositive than lithium, the C—Na bond of these organosodium compounds is best described as

ionic, rather than polar covalent

Treatment of an aldehyde or ketone with either an organolithium or Grignard reagent followed by water forms an

alcohol with a new carbon–carbon bond.

Carbonyl compounds that also contain N—H or O—H bonds undergo an acid–base reaction with

organometallic reagents, not nucleophilic addition

The use of tert-butyldimethylsilyl ether as a protecting group makes possible the synthesis of

4-methyl-1,4- pentanediol from 5-hydroxypentan-2-one

The most useful reactions of organometallic reagents are carried out with esters and acid chlorides, forming either

ketones or 3° alcohols

esters and acid chlorides form 3° alcohols when treated with

two equivalents of either Grignard or organolithium reagents

Acid chlorides, which have the best leaving group Cl− of the carboxylic acid derivatives, react with R’2CuLi to give a

ketone as the product

Esters, which contain a poorer leaving group ( −OR),

do not react with R’2CuLi.

This reaction is called carboxylation

Grignards react with CO2 to give carboxylic acids after protonation with aqueous acid.

Carboxylic acids are compounds containing a

carboxy group (COOH)

The structure of carboxylic acids is often abbreviated as

RCOOH or RCO2H.

The C—O single bond of a carboxylic acid is

shorter than the C—O bond of an alcohol.

(COOH) Because oxygen is more electronegative than either carbon or hydrogen, the C—O and O—H bonds are

polar