Functional Groups - Functional Groups, Their General IUPAC Nomenclature, Practice Problems and FAQs

Everyone enjoys having a variety of flowers and their pleasant smell. Right???

and we are all aware of how these fruits grow. To produce flowers with a variety of fragrances, colors and appearances, different seeds are buried in the soil.

Just like this, when functional groups are added to hydrocarbons in organic chemistry and H is removed, we obtain new molecules with various physical and chemical characteristics.

A functional group is an atom or group of atoms that determines the characteristics of an organic molecule. Each functional group has a distinct identity that is reflected by a unique prefix provided by IUPAC.

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Table of Contents:

Functional groups
IUPAC Nomenclature of Common Functional groups
Aldehydes or Alkanals
Ketones or Alkanones
Carboxylic acid or Alkanoic acid
Acid halide or Alkanoyl Chloride
Acid anhydrides
Ester
Amines or Alkanamines
Alkylcyanide group or Alkanenitrile
Acid Amide or alkanamide
Practice Problems
Frequently Asked Questions

Functional groups:

In the study of organic chemistry, functional groups are the substituent atoms or groups of atoms that are joined to particular molecules.

Chemical reactions that involve two molecules of different sizes but with the same functional groups will behave in a similar way. The same functional group will behave consistently and undergo similar reactions regardless of the chemical in which it is present.

When a molecule has a functional group, it means that its behaviour and chemical reactions may be predictably expected in a systematic way. A functional group is a collection of atoms or bonds that is crucial for a substance's specific chemical reactions.

Also, by comprehending the characteristics of various functional groups, the purposeful execution of chemical reactions to produce a particular compound can be structured.

IUPAC Nomenclature of Common Functional groups:

The common functional groups are discussed in this subsection that must be used in their nomenclature.

In IUPAC, there are three parts to the name of an organic compound:

(i) Word Root

(ii) Prefix

(iii) Suffix

Word root denotes the number of carbon atoms present in the carbon chain.

Chain length	Word root	Chain length	Word root
C₁	Meth	C₇	Hept
C₂	Eth	C₈	Oct
C₃	Prop	C₉	Non
C₄	But	C₁₀	Dec
C₅	Pent	C₁₁	Undec
C₆	Hex	C₁₂	Dodec

Prefix denotes those groups which are not considered as a functional group but treated as substituents in the naming of the organic compounds.

Substituents	Prefix	Substituents	Prefix
-F	Fluoro	-N=N-	Diazo
-Cl	Chloro	-OCH₃	Methoxy
-Br	Bromo	-OCH₂CH₃	Ethoxy
-I	Iodo	-OH	Hydroxy
-NO₂	Nitro	-NH₂	Amino
-NO	Nitroso

There are basically two types of suffix used in the naming of organic compounds:

(i) Primary Suffix

(ii) Secondary Suffix

Primary suffix denotes the nature of linkage in carbon atoms.

If there are all single bonds present in the parent chain, Then the primary suffix ‘ane’ is used.

If there is a double bond present in the parent chain, Then the primary suffix ‘ene’ is used.

If there is a triple bond present in the parent chain, Then the primary suffix ‘yne’ is used.

Secondary suffix denotes the presence of functional groups in the organic compound.

Let us discuss these functional groups one by one–

(i) Aldehydes or Alkanals:

General formula: $C_{n} H_{2 n + 1} C H O$

Representation:

These are derived by replacing the hydrogen atom at the terminal position of a carbon atom with CHO(aldehydic group). The name of alkanals is obtained by using '-al' and replacing 'e' of corresponding alkanes.

Final Name: Alkane -e+ al=Alkanal

Remember one thing while counting the number of carbon atoms in parent chain, carbon of aldehydic group is also included in the numbering.

Aldehyde	IUPAC Name
HCHO	Methanal
CH₃CHO	Ethanal
CH₃CH₂CHO	Propanal
(CH₃)₂CHCHO	2-methylpropanal

(ii) Ketones or Alkanones:

General formula: $C_{n} H_{2 n + 1} C O C_{x} H_{2 x + 1}$

Representation:

These are derived by replacing the hydrogen atom at the non-terminal position of a carbon atom with CO(ketonic group). The name of alkanones is obtained by using '-one' and replacing 'e' of corresponding alkanes.

Final Name: Alkane -e+ one=Alkanone

Remember one thing while counting the number of carbon atoms in the parent chain, carbon of the ketonic group is also included in the numbering.

Ketones	IUPAC Name
CH₃COCH₃	Propanone
CH₂CH₂COCH₃	Butanone
CH₃CH₂COCH₂CH₃	Pentan-3-one
CH₃CH₂CH₂COCH₃	Pentan-2-one
(CH₃)₂CHCOCH₂CH₃	2-methylpentan-3-one

(iii) Carboxylic acid or Alkanoic acid:

General formula: $C_{n} H_{2 n + 1} C O O H$

Representation:

These are derived by replacing the hydrogen atom at the terminal position of a carbon atom with COOH (carboxylic group). The name of alkanoic acid is obtained by using '-oic acid' and replacing 'e' of corresponding alkanes.

Final Name: Alkane -e+ oic acid=Alkanoic acid

Remember one thing while counting the number of carbon atoms in the parent chain, carbon of the carboxylic group is also included in the numbering.

Carboxylic acid	IUPAC Name
HCOOH	Methanoic Acid
CH₃COOH	Ethanoic Acid
CH₂CH₂COOH	Propanoic Acid
CH₃CH₂CH(CH₃)COOH	2-methylbutanoic Acid
(CH₃)₂CHCH₂COOH	3-methylbutanoic Acid

(iv) Acid halide or Alkanoyl Chloride:

General formula: $C_{n} H_{2 n + 1} C O C l$

Representation:

These are derived by replacing the hydrogen atom at the terminal position of a carbon atom with COCl (Acyl chloride group). The name of an acyl chloride is obtained by using '-oyl chloride' and replacing 'e' of corresponding alkanes.

Final Name: $A l k a n e - e + o y l c h l o r i d e = A l k a n o y l c h l o r i d e$

Remember one thing while counting the number of carbon atoms in the parent chain, carbon of acyl chloride group is also included in the numbering.

Acyl Chloride	IUPAC Name
HCOCl	Methanoyl chloride
CH₃COCl	Ethanoyl chloride
CH₂CH₂COCl	Propanoyl chloride
CH₃CH₂CH(CH₃)COCl	2-methylbutanoyl chloride
(CH₃)₂CHCH₂COCl	3-methylbutanoyl chloride

(v) Acid anhydrides:

General formula: R(CO)₂O

Representation:

These are derived from a carboxylic acid by removing one molecule of water.

The name of an acid anhydride is obtained by using '- anhydride' and replacing 'acid' of corresponding carboxylic acid.

Final Name: $A l k a n o i c a c i d - a c i d + a n h y d r i d e = A l k a n o i c A n h y d r i d e$

Acyl Chloride	IUPAC Name
HOCOCOH	Methanoic Anhydride
CH₃OCOCOCH₃	Ethanoic Anhydride
CH₃OCOCOH	Ethanoic Methanoic Anhydride
CH₃OCOCOCH₂CH₃	Ethanoic Propanoic Anhydride

(vi) Ester:

General formula: RCOOR'

Representation:

These are derived from a carboxylic acid by removing -OH group with -OR group.

The name of an ester is obtained by prefixing the name of the alkyl group before the parent chain and using '- oate' and replacing 'ic acid' of corresponding carboxylic acid.

Final Name: $A l k a n o i c a c i d - i c a c i d + a t e = A l k a n o a t e$

Ester	IUPAC Name
HCOOCH₃	Methyl Methanoate
CH₃COOCH₃	Methyl Ethanoate
HCOOCH₂CH₃	Ethyl Methanoate
CH₃COOCH₂CH₃	Ethyl Ethanoate

(vii) Amines or Alkanamines:

General formula: RNH₂

Representation:

These are derived from ammonia by removing one, two or three hydrogen atoms with alkyl substituents.

The name of an amine is obtained by using '- amine' and replacing 'e' of corresponding alkanes.

Final Name: $A l k a n e - e + a m i n e = A l k a n a m i n e$

Amine	IUPAC Name
CH₃NH₂	Methanamine
CH₃CH₂NH₂	Ethanamine
CH₃CH₂NHCH₃	N-methylethanamine
N(CH₃)₃	N,N-dimethylmethanamine

(viii) Alkylcyanide group or Alkanenitrile:

General formula: RCN

Representation:

These are derived by replacing the hydrogen atom at the terminal position of a carbon atom with CN(cyanide group).

The name of an alkyl cyanide is obtained by adding '- nitrile' to the name of corresponding alkanes.

Final Name: $A l k a n e + n i t r i l e = A l k a n e n i t r i l e$

Remember one thing while counting the number of carbon atoms in the parent chain, carbon of alkyl nitrile group is also included.

Amine	IUPAC Name
CH₃CN	Ethanenitrile
CH₃CH₂CN	Propanenitrile
(CH₃)₂CHCN	2-methylpropanenitrile

(ix) Acid Amide or alkanamide:

General formula: RCONH₂

Representation:

These are derived from a carboxylic acid by removing -OH group with -NH₂ group.

The name of an amide is obtained by using '- amide' and replacing 'e' of corresponding alkanes.

Final Name: $A l k a n e - e + a m i d e = A l k a n a m i d e$

Ester	IUPAC Name
HCONH2	Methanamide
CH3CONH2	Ethanamide
CH3CH2CONH2	Propanamide
(CH3)2CHCONH2	2-methylpropanamide

(x) Alcohols or Alkanols:

General formula: $C_{n} H_{2 n + 1} O H$

Representation:

These are derived by replacing the hydrogen atom at the terminal position of a carbon atom with OH(alcohlic group). The name of alkanols is obtained by using '-ol' and replacing 'e' of corresponding alkanes.

Final Name: $A l k a n e - e + o l = A l k a n o l$

Alcohols	IUPAC Name
CH₃OH	Methanol
CH₃CH₂CHO	Propanal
(CH₃)₂CHCHO	2-methylpropanal

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Practice Problems:

Q1. What of the following functional group is present in the given compound?

A. Acid Anhydride
B. Ether
C. Alcohol
D. Ketone

Answer: (D)

Solution: The functional group present in the molecule is the ketonic group and carboxylic acid group. Hence, the correct answer is option (D).

Q2. What will be the correct IUPAC name for the given compound?

A. cyclobutanoyl chloride
B. cyclopentanoyl chloride
C. cyclobutanecarbonyl chloride
D. cyclobutylmethanoyl chloride

Answer: (C)

Solution: There is acyl chloride present in this compound which is a derivative of carboxylic acid. The substituent present with acyl chloride group is cyclobutyl group.

The correct IUPAC name can be written as cyclobutanecarbonyl chloride.

Hence, the correct answer is option (C).

Q3. What will be the correct IUPAC name for the given compound?

A. Phenyl Ethanoic anhydride
B. Benzyl Ethanone
C. Methyl Benzoate
D. Methyl Phenylmethanoate

Answer: (C)

Solution: The functional group given in this compound is the ester group. The name of an ester is obtained by prefixing the name of alkyl group before the parent chain and using '- oate' and replacing 'oic acid' of corresponding carboxylic acid. So, the IUPAC name can be written as Methyl Benzoate. Hence, the correct answer is option (C).

Q4. What will be the correct IUPAC name and functional group present in the given compound?

A. Benzyl Carbanoic Anhydride, Acid Anhydride
B. Benzoic Anhydride, Acid Anhydride
C. Benzyl Benzoate, Ester
D. Benzyl Benzoate, Ester

Answer: (B)

Solution: The given functional group is acid anhydride. These are derived from a carboxylic acid by removing one molecule of water.

The name of an acid anhydride is obtained by using '- anhydride' and replacing 'acid' of corresponding carboxylic acid.

Final Name: $A l k a n o i c a c i d - a c i d + a n h y d r i d e = A l k a n o i c A n h y d r i d e$

Hence, the correct IUPAC name for the given compound is Benzoic Anhydride.

The correct answer is option (B).

Frequently Asked Questions-FAQs:

Q1. What makes understanding a functional group crucial?
Answer: Chemistry places a lot of emphasis on functional groups because they are the parts of molecules that can undergo distinctive reactions. As a result, they control the chemistry and characteristics of many organic molecules. Any compound with carbon and another element is said to be organic.

Q2. Can there be more than one functional group?
Answer: Multiple functional groups are frequently present in a single molecule. In such a scenario, one functional group is regarded as the major functional group, and the other as a substitution. The choice of the functional group is made in a priority sequence.

Carboxylic acid > sulphonic acid > acid anyhydride > ester > acid halide > amide > nitrile > aldehyde > ketone > alcohols > amines

Q3. Is a functional group a double or triple bond?
Answer: Functional groups is a phrase for atoms or groups of atoms inside a molecule that are areas of relatively high reactivity including double and triple bonds. So, yes, Double or triple bonds are also functional groups.

Q4. Do functional groups possess unique characteristics?
Answer: A particular set of atoms with unique characteristics and reactivity is called a functional group. These groups will give their parent compounds numerous similarities irrespective of the additional atoms that are involved.