Chiral carbon

5
1-4 Formatıon of Cyanohydrıns 7
1-5 Addıtıon of Sulfur Nucleophıles 8
1-6 Addıtıon of Carbon Nucleophıles 9
1-7 Addıtıon of 1 Amınes (formatıon of ımıne) 9
1-8 Addıtıon of 2 Amınes (Formatıon of Enamınes) 10
1-9 Hydratıon 12
1-10 Addıtıon of Peroxyacıd 13
1-11 The Wıttıg Reactıon 14 REFERENCES 16

a carbonyl group. An aldehyde contains at least one H atom bonded to the carbonyl carbon, whereas a ketone has two alkyl or aryl groups bonded to it

An aldehyde is often written as RCHO. Remember that the H atom is bonded to the carbon atom, not the oxygen. Likewise, a ketone is written as RCOR, or if both alkyl groups are the same, R2CO. Each structure must contain a C––O for every atom to have an octet.: v Two structural features determine the chemistry and properties of aldehydes and ketones.

it relatively uncrowded. • The electronegative oxygen atom polarizes the carbonyl group, making the carbonyl carbon electrophilic. As a result, aldehydes and ketones react with nucleophiles. The relative reactivity of the carbonyl group is determined by the number of R groups bonded to it. As the number of R groups around the carbonyl carbon increases, the reactivity of the carbonyl compound decreases, resulting in the following order of reactivity:

Increasing the number of alkyl groups on the carbonyl carbon decreases reactivity for both steric and electronic reasons, as discussed in Section 20.2B.

similar in structure in that both classes of compounds possess a CRO bond, called a carbonyl group

The carbonyl group of an aldehyde is flanked by a hydrogen atom, while the carbonyl group of a ketone is flanked by two carbon atoms. Aldehydes and ketones are responsible for many flavor and odors that you will readily recognize:

and testosterone, the female and male sex hormones

Simple aldehydes and ketones are industrially important; for example:

Acetone is used as a solvent and is commonly found in nail polish remover, while formaldehyde is used as a preservative in some vaccine formulations. Aldehydes and ketones are also used as building blocks in the syntheses of commercially important compounds, including pharmaceuticals and polymers. Compounds containing a carbonyl group react with a large variety of nucleophiles, affording a wide range of possible products. Due to the versatile reactivity of the carbonyl group, aldehydes and ketones occupy a central role in organic chemistry.

our discussion of carbonyl reactions by looking at the two general kinds of reactions that aldehydes and ketones undergo. [1] Reaction at the carbonyl carbon electrophilic carbonyl carbon makes aldehydes and ketones susceptible to nucleophilic addition reactions. The elements of H and Nu are added to the carbonyl group.

[2] Reaction at the ` carbon
Enolates are nucleophiles, and so they react with electrophiles to form new bonds on the ` carbon
Aldehydes and ketones react with nucleophiles at the carbonyl carbon.
Aldehydes and ketones form enolates that react with electrophiles at the ` carbon.

are usually drawn for nucleophilic addition, depending on the nucleophile (negatively charged versus neutral) and the presence or absence of an acid catalyst. With negatively charged nucleophiles, nucleophilic addition follows the two-step process General Mechanism—Nucleophilic Addition (1)

General Mechanism—Acid-Catalyzed Nucleophilic Addition (1)

liquid that boils at 26 °C. Because it is mildly acidic, HCN is sometimes called hydrocyanic acid. The conjugate base of hydrogen cyanide is the cyanide ion Cyanide ion is a strong base and a strong nucleophile. It attacks ketones and aldehydes to give addition products called cyanohydrins. The mechanism is a base-catalyzed nucleophilic addition, as shown in Mechanism 18-4. Cyanide ion attacks the carbonyl group, forming an alkoxide ion that protonates to give the cyanohydrin.

Mechanısm -Formation of Cyanohydrins

ketones react with thiols (the sulfur analogues of alcohols) The mechanism for the addition of a thiol is the same as the mechanism for the addition of an alcohol Thioacetal formation is useful in organic synthesis because a thioacetal is desulfurized when it reacts with H2 and Raney nickel. Desulfurization replaces the C—S bonds with C—H bonds.

Thus, thioacetal formation followed by desulfurization provides a way to convert a carbonyl grou into a methylene group.

Reagents When treated with a Grignard reagent, aldehydes and ketones are converted into alcohols, accompanied by the formation of a new C!C bond: The mechanism of action for these reagents has been heavily investigated and is fairly complex

1-7 Addition of 1° Amines ( Formation of Imine) (1)
We now move on to the reaction of aldehydes and ketones with nitrogen and oxygen hetero atoms. Amines, for example, are organic nitrogen compounds that contain a nonbonded electron pair on the N atom. Amines are classifi ed as 1°, 2°, or 3° by the number of alkyl groups bondedto the nitrogen atom

imine is surrounded by three groups (two atoms and a lone pair), it is sp2 hybridized, making the C –N– R" bond angle ~120° (not 180°). Imine formation is fastest when the reaction medium is weakly acidic

Amin( Formation of Enamines) (1)
A 2° amine reacts with an aldehyde or ketone to give an enamine. Enamines have a nitrogen atom bonded to a double bond (alkene + amine = enamine)

a ketone or an aldehyde is in equilibrium with its hydrate, a geminal diol. With most ketones, the equilibrium favors the unhydrated keto form of the carbonyl.

MECHANISM-Hydration of Ketones and Aldehydes In Acıd

the carbonyl group. In acidic conditions, strong nucleophiles are rarely present. An acid (or Lewis acid) usually protonates the carbonyl to activate it toward attack by a weak nucleophile.

Aldehydes and ketones react with the conjugate base of a peroxyacid to form carboxylic acids and esters, respectively. Recall that a peroxyacid contains one more oxygen than a carboxylic acid and it is this oxygen that is inserted between the carbonyl carbon and the H of an aldehyde or the R of a ketone (see the top of the next page). The reaction is called a Baeyer–Villiger oxidation. It is an Oxidation reaction because the number of C¬O bonds increases. A particularly good reagent for a Baeyer–Villiger oxidation is peroxytrifluoroacetate ion

If the two alkyl substituents attached to the carbonyl group of the ketone are different, thenon what side of the carbonyl carbon is the oxygen inserted? For example, does the oxidation of cyclohexyl methyl ketone form methyl cyclohexanecarboxylate or cyclohexyl acetate?

The Wittig reaction uses phosphorus ylides (called Wittig reagents ) to convert aldehydes and ketones to alkenes

Wittig reactions may be carried out in a number of different solvents; normally tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO) is used.