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Difference Between Aldehyde and Ketone

Aldehyde vs Ketone

Aldehydes and ketones are known as organic molecules with a carbonyl group. In a carbonyl group, carbon atom has a double bond to oxygen. The carbonyl carbon atom is sp2 hybridized.  So, aldehydes and ketones have a trigonal planar arrangement around the carbonyl carbon atom. The carbonyl group is a polar group, thus, aldehydes and ketones have higher boiling points compared to the hydrocarbons having the same weight. But these cannot make stronger hydrogen bonds like alcohols resulting lower boiling points than the corresponding alcohols. Because of the hydrogen bond formation ability, low molecular weight aldehydes and ketones are soluble in water. But when the molecular weight increases, they become hydrophobic. The carbonyl carbon atom is partially positive charged, hence can act as an electrophile. Therefore, these molecules are easily subjected to nucleophilic substitution reactions. The hydrogens attached to the carbon; next to the carbonyl group has acidic nature, which accounts for various reactions of aldehydes and ketones.

Aldehyde

Aldehydes have a carbonyl group. This carbonyl group is bonded to another carbon from one side, and from the other end, it is connected to hydrogen. Therefore, aldehydes can be characterized with the –CHO group, and following is the general formula of an aldehyde.

The simplest aldehyde is formaldehyde. However, this is deviated from the general formula by having a hydrogen atom instead of R group. In the nomenclature of aldehyde, according to the IUPAC system “al” is used to denote an aldehyde. For aliphatic aldehydes, the “e” of the corresponding alkane is replaced with “al”. For example, CH3CHO is named as ethanal, and CH3CH2CHO is named as propanal. For aldehydes with ring systems, where the aldehyde group is directly attached to the ring, “carbaldehyde” term is used as a suffix to name them. But C6H6CHO is commonly known as benzaldehyde rather than using benzenecarbaldehyde.

Aldehydes can be synthesized by various methods. One method is by oxidizing primary alcohols. Moreover, aldehydes can be synthesized by reducing esters, nitriles and acyl chlorides.

Ketone

In ketones carbonyl group is situated between two carbon atoms. General formula of a ketone is a follows.

“one” is the suffix used in ketone nomenclature. Instead of –e of the corresponding alkane “one” is used. The aliphatic chain is numbered in a way that gives the carbonyl carbon the lowest possible number. For example, CH3COCH2CH2CH3 is named as 2-pentanone. Ketones can be synthesized from the oxidation of secondary alcohols, by ozonolysis of alkenes, etc. ketones have the ability to undergo keto-enol tautomerism. This process happens, when a strong base takes up the α-hydrogen (hydrogen attached to the carbon, which is next to the carbonyl group). The ability to release the α-hydrogen, makes ketones more acidic than corresponding alkanes.

What is the difference between Aldehyde and Ketone?

- The carbonyl group of aldehyde is bonded to a hydrogen from one end, but in ketone, the carbonyl group is bonded to carbon atoms from both sides.

- Therefore, a ketone functional group is always seen in the middle of a molecule, and aldehyde group is always at a termini.

- In the nomenclature, aldehydes have the suffix –al and for ketones the suffix is –one.

- In a molecule where aldehyde is the functional group, the carbonyl carbon is given the number one in nomenclature. In ketone, the chain is numbered in a way to give the lowest possible number to the carbonyl carbon (it won’t get number one at any occasion).

- Aldehyde can be easily oxidized compared to ketones.


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