Question

Name the following halides according to IUPAC system and classify them as alkyl, allyl, benzyl (primary, secondary, tertiary). vinyl or aryl halides: (i) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}(\mathrm{Cl}) \mathrm{CH}_{3}\) (ii) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CH}\left(\mathrm{C}_{2} \mathrm{H}_{5}\right) \mathrm{Cl}\) (iii) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}_{2} \mathrm{I}\) (iv) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2} \mathrm{CH}(\mathrm{Br}) \mathrm{C}_{6} \mathrm{H}_{5}\) (v) \(\mathrm{CH}_{3} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_{3}\) (vi) \(\mathrm{CH}_{3} \mathrm{C}\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{CH}_{2} \mathrm{Br}\) (vii) \(\mathrm{CH}_{3} \mathrm{C}(\mathrm{Cl})\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\right.\) (viii) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{C}(\mathrm{Cl}) \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\) (ix) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHC}(\mathrm{Br})\left(\mathrm{CH}_{3}\right)_{2}\) (x) \(p-\mathrm{ClC}_{6} \mathrm{H}_{4} \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\) (xi) \(\mathrm{m}-\mathrm{Cl} \mathrm{CH}_{2} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{CH}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{3}\) (xii) \(\mathrm{o}-\mathrm{Br}-\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2} \mathrm{CH}_{3}\)

Short answer

(i) 2-chloro-2-methylpropane (tert-alkyl halide), (ii) 4-chloro-3-ethylpentane (sec-alkyl halide), (iii) 4-iodo-3-methylpentane (prim-alkyl halide), (iv) 3-bromo-3,3-dimethylbenzylpropane (prim-benzyl halide), (v) 2-bromo-3-methylbutane (sec-alkyl halide), (vi) 1-bromo-2,2-diethylpropane (prim-alkyl halide), (vii) 2-chloro-2-ethylpropane (tert-alkyl halide), (viii) 1-chloro-3,3-dimethyl-1-butene (vinyl), (ix) 3-bromo-3-methyl-1-butene (allylic), (x) p-chloro-α,α-dimethylbenzylmethane (benzyl), (xi) m-chloro-3,3-dimethylbenzylpropane (benzyl), (xii) o-bromoethylbenzene (aryl).

Step-by-step solution

Recognizing the Structure

First, identify the carbon chain and the location of the halide for each molecule. Examine the structure to classify the compound based on the type of carbon-halogen bond (as alkyl, allyl, benzyl, vinyl, or aryl).

Naming Structure (i)

The structure is \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}(\mathrm{Cl}) \mathrm{CH}_{3}\). This indicates a four-carbon chain with a chlorine atom attached to the second carbon, resulting in the name 2-chloro-2-methylpropane, which is a tertiary alkyl halide.

Naming Structure (ii)

The structure is \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{CH}_{3}) \mathrm{CH}(\mathrm{C}_{2} \mathrm{H}_{5}) \mathrm{Cl}\). This is a five-carbon chain with chlorine at the fourth position; thus it is named 4-chloro-3-ethylpentane, a secondary alkyl halide.

Naming Structure (iii)

The structure is \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{C}(\mathrm{CH}_{3})_{2} \mathrm{CH}_{2} \mathrm{I}\). As a five-carbon chain with iodine on the fourth carbon, the name is 4-iodo-3-methylpentane, a primary alkyl halide.

Naming Structure (iv)

The structure is \((\mathrm{CH}_{3})_{3} \mathrm{CCH}_{2} \mathrm{CH}(\mathrm{Br}) \mathrm{C}_{6} \mathrm{H}_{5}\). This is benzylic due to the presence of a benzyl group, named as 3-bromo-3,3-dimethylbenzylpropane, a primary benzyl halide.

Naming Structure (v)

The structure is \(\mathrm{CH}_{3} \mathrm{CH}(\mathrm{CH}_{3}) \mathrm{CH}(\mathrm{Br}) \mathrm{CH}_{3}\). A four-carbon chain with bromine at the third position, giving the name 2-bromo-3-methylbutane, a secondary alkyl halide.

Naming Structure (vi)

The structure is \(\mathrm{CH}_{3} \mathrm{C}(\mathrm{C}_{2} \mathrm{H}_{5})_{2} \mathrm{CH}_{2} \mathrm{Br}\). This forms a primary alkyl halide, named 1-bromo-2,2-diethylpropane.

Naming Structure (vii)

The structure is \(\mathrm{CH}_{3} \mathrm{C}(\mathrm{Cl})(\mathrm{C}_{2} \mathrm{H}_{5})_{2}\). This is a tertiary alkyl halide and named 2-chloro-2-ethylpropane.

Naming Structure (viii)

The structure is \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{C}(\mathrm{Cl}) \mathrm{CH}_{2} \mathrm{CH}(\mathrm{CH}_{3})_{2}\). This is a vinyl halide, named 1-chloro-3,3-dimethyl-1-butene.

Naming Structure (ix)

The structure is \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHC}(\mathrm{Br})(\mathrm{CH}_{3})_{2}\). This is an allylic halide and named 3-bromo-3-methyl-1-butene.

Naming Structure (x)

The structure is \(\mathrm{p-ClC}_{6} \mathrm{H}_{4} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{CH}_{3})_{2}\). It is a benzyl halide because the halide is on the benzyl carbon, and is named p-chloro-α,α-dimethylbenzylmethane.

Naming Structure (xi)

The structure is \(\mathrm{m}-\mathrm{Cl} \mathrm{CH}_{2} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{CH}_{2} \mathrm{C}(\mathrm{CH}_{3})_{3}\). It possesses a meta position chlorine on the benzyl ring and is named m-chloro-3,3-dimethylbenzylpropane.

Naming Structure (xii)

The structure is \(\mathrm{o}-\mathrm{Br}-\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{CH}(\mathrm{CH}_{3}) \mathrm{CH}_{2} \mathrm{CH}_{3}\). With bromine in the ortho position, it is an aryl halide, named o-bromoethylbenzene.

Key concepts

Alkyl Halides

Alkyl halides, also known as haloalkanes, are compounds where a halogen atom is bonded to an aliphatic carbon. An aliphatic carbon refers to carbons in linear, branched, or cyclic structures that are not aromatic. These can be further classified as primary, secondary, or tertiary based on the carbon to which the halogen is attached.
A primary alkyl halide has the halogen bonded to a carbon connected to only one other carbon. Secondary alkyl halides have the halogen on a carbon bonded to two other carbons, while tertiary alkyl halides have their halogen bonded to a carbon that is connected to three other carbons.

• Example of a primary alkyl halide: Propyl bromide (CH₃CH₂CH₂Br).
• Example of a secondary alkyl halide: Isopropyl chloride ((CH₃)₂CHCl).
• Example of a tertiary alkyl halide: Tert-butyl iodide ((CH₃)₃CI).

Aryl Halides

Aryl halides are organic compounds containing a halogen atom directly attached to an aromatic ring. The presence of the aromatic ring plays a crucial role in their behavior and reactivity. Unlike alkyl halides, aryl halides have the halogen bonded to a carbon atom of a benzene ring, which makes them less reactive towards typical nucleophilic substitutions compared to alkyl halides.
Aryl halides are crucial in the synthesis of various pharmaceuticals, dyes, and agrochemicals due to their unique chemical properties. Some common aryl halides include chlorobenzene, bromobenzene, and iodobenzene.

• One significant challenge in working with aryl halides is overcoming their relative stability, which requires specific conditions for reactions.

IUPAC Naming System

The International Union of Pure and Applied Chemistry (IUPAC) naming system provides a standardized way to name chemical compounds, ensuring clarity and consistency across scientific disciplines. It is essential for accurately identifying compounds since common names may vary in different regions or industries.
When naming halides using the IUPAC system, following key steps are observed:

• Identify the longest carbon chain as the parent chain and number it such that the substituents receive the lowest possible number.
• Name and number the substituents as prefixes, such as "chloro" or "bromo," depending on the halogen present.
• The halide group is identified with its position on the carbon chain.

This systematic naming allows chemists worldwide to communicate complex chemical structures unambiguously.

Structure Recognition

Structure recognition in organic chemistry is crucial for understanding molecule identification and nomenclature. This involves determining the type of carbon framework and identifying functional groups in a compound.
For halides, recognizing the structure involves:

• Identifying the longest carbon chain to determine the parent hydrocarbon.
• Locating the position of the halide group within the structure.
• Understanding the structural features such as whether a compound is aliphatic, aromatic, linear, or branched.

Structure recognition is key to correctly classifying compounds and applying the appropriate naming rules. It's the foundational step in solving nomenclature problems.

Organic Chemistry Classification

In organic chemistry, compounds are classified based on their molecular structure and functional groups, which defines their chemical behavior. Halides fall into this classification as they introduce functional groups where a halogen atom replaces a hydrogen atom. Depending on the type of carbon-halogen bond and the surrounding carbon skeleton, halides can be segmented into different categories:

• Alkyl Halides: Halogen bonded to aliphatic carbon.
• Aryl Halides: Halogen bonded to aromatic carbon.
• Vinyl Halides: Halogen bonded to a sp²-hybridized carbon in a double bond.
• Allyl Halides: Halogen bonded to the carbon adjacent to a carbon-carbon double bond.
• Benzyl Halides: Halogen bonded to the carbon attached to a benzene ring.

Understanding these classifications aids in predicting the reactivity and properties of the compounds.