Question

How many of the following sets are member of same homologous series? (i) \(\mathrm{C}_{2} \mathrm{H}_{6}, \mathrm{C}_{4} \mathrm{H}_{10}, \mathrm{C}_{6} \mathrm{H}_{12}\) (ii) \(\mathrm{CH}_{-} \mathrm{COOH}, \mathrm{CH}_{1} \mathrm{CH}, \mathrm{COO} \mathrm{H}_{\mathrm{CH}}, \mathrm{CH}_{-}-\mathrm{CH}_{2}-\mathrm{COOH}\) (iii) \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{Br}, \mathrm{C}_{4} \mathrm{H}_{9} \mathrm{Br}, \mathrm{C}_{6} \mathrm{H}_{13} \mathrm{Br}\) (iv) \(\mathrm{CH}_{1} \mathrm{CHO}, \mathrm{Cll}_{1} \mathrm{CH}_{2} \mathrm{CHO}, \mathrm{CH}_{6} \mathrm{COCH}_{2} \mathrm{CH}_{1}\) (v) Cc1ccc(O)cc1 (vi) \(\mathrm{CH}_{3}-\mathrm{NH}_{2}, \mathrm{CH}_{3}-\mathrm{NH}-\mathrm{CH}_{3}, \mathrm{~N}\left(\mathrm{CH}_{3}\right)_{3}\) (vii) \(\mathrm{CH}_{2}=\mathrm{CH}_{2}, \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}, \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}=\mathrm{CH}_{2}\) (viii) \(\mathrm{CH}_{3}-\mathrm{OH}\), COCCOCC(C)O

Short answer

Sets (i), (iii), (vi), and (vii) belong to the same homologous series.

Step-by-step solution

(i) Alkanes

In this set: \(\mathrm{C}_{2} \mathrm{H}_{6}, \mathrm{C}_{4} \mathrm{H}_{10}, \mathrm{C}_{6} \mathrm{H}_{12}\). All three compounds have the general formula \(\mathrm{C}_{n}\mathrm{H}_{2n+2}\), which corresponds to the alkanes. Therefore, they belong to the same homologous series.

(ii) Carboxylic acids and alkynes

In this set: \(\mathrm{CH}_{-} \mathrm{COOH}, \mathrm{CH}_{1} \mathrm{CH}, \mathrm{COO} \mathrm{H}_{\mathrm{CH}}, \mathrm{CH}_{-}-\mathrm{CH}_{2}-\mathrm{COOH}\). The compounds have different general formulas and don't belong to any single homologous series.

(iii) Alkyl bromides

In this set: \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{Br}, \mathrm{C}_{4} \mathrm{H}_{9} \mathrm{Br}, \mathrm{C}_{6} \mathrm{H}_{13} \mathrm{Br}\). All three compounds have the general formula \(\mathrm{C}_{n}\mathrm{H}_{2n+1}\mathrm{Br}\), which corresponds to the alkyl bromides. Therefore, they belong to the same homologous series.

(iv) Aldehydes and others

In this set: \(\mathrm{CH}_{1} \mathrm{CHO}, \mathrm{Cll}_{1} \mathrm{CH}_{2} \mathrm{CHO}, \mathrm{CH}_{6} \mathrm{COCH}_{2} \mathrm{CH}_{1}\). The compounds have different general formulas and don't belong to any single homologous series.

(v) Aromatic compound

In this set: Cc1ccc(O)cc1. There is only one compound given, so there is no homologous series to compare it with here. This compound is aromatic in nature, but we cannot find more than one compound to form a homologous series.

(vi) Amines

In this set: \(\mathrm{CH}_{3}-\mathrm{NH}_{2}, \mathrm{CH}_{3}-\mathrm{NH}-\mathrm{CH}_{3}, \mathrm{~N}\left(\mathrm{CH}_{3}\right)_{3}\). All three compounds belong to the amine functional group with the general formula \(\mathrm{R}_{n}\mathrm{N}\). They belong to the same homologous series.

(vii) Alkenes

In this set: \(\mathrm{CH}_{2}=\mathrm{CH}_{2}, \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}_{2}, \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}=\mathrm{CH}_{2}\). All three compounds have the general formula \(\mathrm{C}_{n}\mathrm{H}_{2n}\), which corresponds to alkenes. Therefore, they belong to the same homologous series.

(viii) Alcohols and others

In this set: \(\mathrm{CH}_{3}-\mathrm{OH}\), COCCOCC(C)O. The compounds have different general formulas and do not belong to any single homologous series. In conclusion, sets (i), (iii), (vi), and (vii) belong to the same homologous series.

Key concepts

Alkanes

Alkanes are a fascinating group of hydrocarbons. They are also known as paraffins. Alkanes are the simplest type of hydrocarbon, consisting only of carbon and hydrogen atoms connected by single bonds. This creates a saturated hydrocarbon, meaning they contain the maximum possible number of hydrogen atoms for each carbon atom. The general formula for alkanes is \( C_nH_{2n+2} \). For example, methane (omenclature{CH_4}) is the simplest alkane. Other members of the alkane family include ethane \( (C_2H_6) \) and propane \( (C_3H_8) \).

• They are typically nonpolar and thus do not mix well with water, making them good lubricants and fuels.
• They undergo combustion reactions, which are essential for energy production.

Carboxylic Acids

Carboxylic acids stand out due to their functional group, the carboxyl group (-COOH). They are organic compounds with both a carbonyl and a hydroxyl group attached to the same carbon atom. This results in their acidic properties, allowing them to donate protons in chemical reactions. The general formula is \( R-COOH \), where \( R \) is a hydrocarbon group.

• The simplest carboxylic acid is formic acid \( (HCOOH) \), followed by acetic acid \( (CH_3COOH) \), which is used in vinegar.
• Carboxylic acids are crucial in biological systems, and they serve as building blocks in the synthesis of esters and amides.

Alkyl Bromides

In the world of organic chemistry, alkyl bromides are compounds where a bromine atom is bonded to an alkyl group. This family is characterized by the general formula \( C_nH_{2n+1}Br \). The presence of the bromine atom makes these compounds more reactive than their alkane counterparts.

• Alkyl bromides are often used as intermediates in the synthesis of other organic compounds due to their reactivity.
• They are also used in the development of pharmaceuticals as well as in other chemical industries.

Amines

Amines are nitrogen-containing compounds derived from ammonia \( (NH_3) \) by replacing one or more hydrogen atoms with alkyl or aryl groups. They can be categorized based on the number of carbon groups attached to the nitrogen atom: primary, secondary, or tertiary amines. Their general formula is \( R_nNH_{3-n} \).

• Amines are prevalent in biological systems, they act as neurotransmitters and hormones.
• The distinctive fishy smell associated with decay is partly due to volatile amines.

Alkenes

Alkenes, or olefins, are hydrocarbons characterized by the presence of at least one carbon-carbon double bond, making them unsaturated. The simplest alkene is ethylene \( (C_2H_4) \). The general formula for alkenes is \( C_nH_{2n} \). The double bond allows alkenes to participate in a variety of chemical reactions, making them quite reactive.

• Alkenes are used as starting materials in the synthesis of polymers and other chemicals.
• They play a key role in the petrochemical industry.

Alcohols

Alcohols are organic compounds with one or more hydroxyl groups \((-OH)\) attached to a carbon atom. They follow the general formula \( R-OH \), where \( R \) is a hydrocarbon group. The simplest alcohol is methanol \( (CH_3OH) \), commonly known as wood alcohol.

• Alcohols are used in beverages, as solvents, and as intermediates in chemical reactions.
• They are essential in the production of hand sanitizers and antiseptics.

Aromatic Compounds

Aromatic compounds, historically known for their pleasant smells, are characterized by a special type of stability due to resonance. This classification includes benzene and its derivatives, which contain a ring of six carbon atoms with alternating double bonds. Aromatic compounds are represented by the formula \( C_nH_m \) but often include complex cyclic structures.

• An understanding of aromatic compounds is essential in fields such as pharmaceuticals, where modification of these structures can lead to potent medications.
• The term "aromatic" is derived from the natural sources from which these compounds were first isolated.