Aldehydes, ketones and carboxylic acids

Question 1

importance of ald, ketones and carbo acids

Answer 1

Aldehydes, ketones and carboxylic acids are widespread in plants
and animal kingdom. They play an important role in biochemical
processes of life. They add fragrance and flavour to nature, for example,
vanillin (from vanilla beans), salicylaldehyde (from meadow sweet) and
cinnamaldehyde (from cinnamon) have very pleasant fragrances.
They are used in many food products and pharmaceuticals to add
flavours. Some of these families are manufactured for use as solvents
(i.e., acetone) and for preparing materials like adhesives, paints, resins,
perfumes, plastics, fabrics, etc.

Question 2

common name of aldehydes

Answer 2

The common names of most aldehydes are
derived from the common names of the corresponding carboxylic
acids [Section 8.6.1] by replacing the ending –ic of acid with aldehyde.
At the same time, the names reflect the Latin or Greek term for the
original source of the acid or aldehyde. The location of the substituent
in the carbon chain is indicated by Greek letters a, b, g, d, etc. The
a-carbon being the one directly linked to the aldehyde group, bcarbon the next, and so on.

Question 3

common name of ketones

Answer 3

The common names of ketones are derived by naming two alkyl
or aryl groups bonded to the carbonyl group. The locations of
substituents are indicated by Greek letters, a a’, b b’ and so on
beginning with the carbon atoms next to the carbonyl group,
indicated as aa¢. Some ketones have historical common names,
the simplest dimethyl ketone is called acetone. Alkyl phenyl
ketones are usually named by adding the name of acyl group as
prefix to the word phenone.

Question 4

describe the structure of carbonyl group

Answer 4

The carbonyl carbon atom is sp
2
-hybridised and forms three sigma (s)
bonds. The fourth valence electron of carbon remains in its p-orbital
and forms a p-bond with oxygen by overlap with p-orbital of an oxygen.
In addition, the oxygen atom also has two non bonding electron pairs.
Thus, the carbonyl carbon and the three atoms attached to it lie in the
same plane and the p-electron cloud is above and below this plane. The
bond angles are approximately 120° as expected of a trigonal coplanar
structure

Question 5

card

Question 6

physical state of ketones, aldehydes

Answer 6

Methanal is a gas at room temperature. Ethanal is a volatile liquid.
Other aldehydes and ketones are liquid or solid at room temperature.

Question 7

describe bpts of aldehydes and ketones

Answer 7

The boiling points of aldehydes and ketones are higher than
hydrocarbons and ethers of comparable molecular masses. It is due to
weak molecular association in aldehydes and ketones arising out of the
dipole-dipole interactions. Also, their boiling points are lower than those
of alcohols of similar molecular masses due to absence of intermolecular
hydrogen bonding.

Question 8

describe the solubility of cpds in water?

Answer 8

The lower members of aldehydes and ketones such as methanal,
ethanal and propanone are miscible with water in all proportions,
because they form hydrogen bond with water.

However, the solubility of aldehydes and ketones decreases rapidly
on increasing the length of alkyl chain.

All aldehydes and ketones are
fairly soluble in organic solvents like benzene, ether, methanol,
chloroform, etc.

Question 9

what is the smell of aldehydes

Answer 9

The lower aldehydes have sharp pungent odours. As
the size of the molecule increases, the odour becomes less pungent
and more fragrant. In fact, many naturally occurring aldehydes and
ketones are used in the blending of perfumes and flavouring agents.