Question

Give the common name for each of the following organic halides: (a) \(\mathrm{CH}_{3}-\mathrm{I}\) (b) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Br}\) (c) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{F}\) (d) \(\left(\mathrm{CH}_{3}\right)_{2}-\mathrm{CH}-\mathrm{Cl}\)

Short answer

(a) Methyl iodide, (b) Ethyl bromide, (c) Propyl fluoride, (d) Isopropyl chloride.

Step-by-step solution

Identify Structure of Compound (a)

The compound given is \( \mathrm{CH}_{3}-\mathrm{I} \). This structure consists of a methyl group \( (\mathrm{CH}_{3}) \) attached to an iodine atom. The configuration directly indicates that it is a methyl iodide.

Identify Structure of Compound (b)

The compound given is \( \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{Br} \). This structure consists of an ethyl group \( (\mathrm{CH}_{3}-\mathrm{CH}_{2}) \) attached to a bromine atom. This structure is commonly referred to as ethyl bromide.

Identify Structure of Compound (c)

The compound given is \( \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{F} \). This involves a propyl group \( (\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}) \) bonded to a fluorine atom. This configuration is known as propyl fluoride.

Identify Structure of Compound (d)

The compound given is \( (\mathrm{CH}_{3})_{2}-\mathrm{CH}-\mathrm{Cl} \). This molecule has an isopropyl group \( ((\mathrm{CH}_{3})_{2}-\mathrm{CH}) \) linked to a chlorine atom. The common name for this arrangement is isopropyl chloride.

Key concepts

IUPAC nomenclature

The International Union of Pure and Applied Chemistry (IUPAC) provides a systematic way of naming chemical compounds to ensure clear communication among scientists worldwide. The IUPAC nomenclature for organic halides involves several steps for accurately identifying the compound.

• **Identify the longest carbon chain:** In organic halides, the main chain is marked by the longest continual chain of carbon atoms. This determines the base name for the organic molecule.
• **Number the carbon atoms:** Start numbering from the end nearest to the halogen substituent. This helps in assigning the lowest possible number to the halogen atom.
• **Attach the halogen name as a prefix:** The halogen is named as a prefix to the main chain with the position number. Common halogens include fluoro, chloro, bromo, and iodo for fluorine, chlorine, bromine, and iodine, respectively.

By following these guidelines, an organic compound like CH₃-CH₂-Br is termed as 1-bromoethane in IUPAC nomenclature, indicating that bromine is attached to the first carbon of an ethane chain.
This systematized approach helps avoid confusion common with different traditional names.

Functional groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristics and chemical reactions of those molecules. In the context of organic halides, the functional group is primarily the halogen attached to the carbon skeleton.

• **Halogens as Functional Groups:** Halogens determine the properties of the organic halide, influencing its reactivity, boiling point, and solubility. Depending on their position, they introduce polarization due to their electronegativity.
• **Impact on Chemical Behavior:** The presence of halogens in organic compounds affects both physical and chemical properties. They can activate or deactivate other functional groups within the molecule, impacting the overall reactivity.

Organic halides like CH₃-CH₂-CH₂-F show distinct properties due to the fluorine atom, which acts as a point of interest for reactions like substitution or elimination.

Common names in chemistry

Common names are the informal or traditional names for chemicals and often less systematic than IUPAC names. They are typically derived from the source of the compound or its traditional usage.

• **Usage of Common Names:** Common names are widely used in industry, education, and everyday conversation. For instance, the common name for CH₃-I is methyl iodide, derived from combining the group's name (methyl) with the halide (iodide).
• **Historical Context:** They often reflect historical naming practices leaving a legacy in the field, such as isopropyl chloride for (CH₃)₂-CH-Cl, where 'isopropyl' emphasizes the branched structure.

While they may not be as detailed as IUPAC nomenclature, common names provide a quick reference to the identity of a substance. These names are especially useful when discussing compounds with known or standard formulations, easing understanding and communication.