Problem 202 - A Complete Resource Book in Chemistry for JEE Main

Question

The IUPAC name of (a) 3, 3-dimethyl-1-hydroxycyclohexane (b) 1,1 -dimethyl-3-hydroxycyclohexane (c) 3,3 -dimethyl-1-cyclohexanol (d) 1, 1 -dimethyl-3-cyclohexanol

Step-by-Step Solution

Answer

(c) 3,3-dimethyl-1-cyclohexanol

Step 1: Analyzing the Compound

3,3-dimethyl-1-hydroxycyclohexane consists of a cyclohexane ring with hydroxy and two methyl groups. The presence of the hydroxy group suggests an alcohol functional group.

Step 2: Identifying the Functional Group Position

Since the hydroxy group is considered at position 1 (hence '1-cyclohexanol'), it indicates the primary numbering regards the alcohol functional group. Positions for other substituents are counted from the carbon bearing the hydroxy group.

Step 3: Locating Additional Substituents

There are two methyl groups situated on the third carbon (hence '3,3-dimethyl'), indicating the full structure to be a cyclohexanol with dimethyl groups on carbon 3.

Step 4: Writing the IUPAC Name

In IUPAC nomenclature, the hydroxy group is prioritized, and its presence is indicated by the suffix '-ol.' Concurrent substituents are included as prefixes: the compound is named 3,3-dimethyl-1-cyclohexanol.

Key Concepts

Understanding Cyclohexane

Cyclohexane is a fundamental structure in organic chemistry. It consists of six carbon atoms forming a ring, making it a type of cycloalkane. Cyclohexane's ring structure gives it unique chemical properties compared to straight-chain alkanes. Although it seems like a flat hexagon, cyclohexane possesses a more stable three-dimensional shape known as the "chair" conformation.
This conformation minimizes steric strain and is the most stable among possible forms, contributing to the stability of molecules like cyclohexanol.

• Cyclohexane's flexibility allows various atoms or groups to attach as substituents, changing its chemical behavior.
• Because the carbon ring doesn't have double bonds, cyclohexane is saturated, meaning it has the maximum number of hydrogen atoms attached to its carbon skeleton without forming double bonds.

Understanding cyclohexane forms the foundation for grasping more complex molecules like cyclohexanol, where substituents are added to cyclohexane.

Exploring Alcohol Functional Groups

The alcohol functional group is characterized by the presence of an -OH group, often referred to as a hydroxyl group. In IUPAC naming, alcohols take priority, and the suffix '-ol' is added to the main carbon structure to indicate their presence. For instance, cyclohexanol refers to cyclohexane that has been modified to include a hydroxyl group.
When naming compounds with an alcohol group, the carbon bearing the hydroxyl group is given the lowest possible number.

• This is due to the alcohol group having a higher priority than other common substituents like halogens or alkyl groups.
• The hydroxyl group affects the molecule's polarity and solubility, generally making alcohols more hydrophilic than their alkane counterparts.

This ability to alter polarity is crucial in both biological systems and industrial applications, demonstrating the functional significance of alcohol groups.

The Role of Methyl Substituents

Methyl groups are among the simplest alkyl groups, consisting of one carbon atom bonded to three hydrogen atoms ( (CH_3) ). In organic chemistry, these groups are common substituents that can significantly impact the physical and chemical properties of a molecule.
In IUPAC nomenclature, the presence of methyl groups is noted by the prefix 'methyl' followed by their position numbers on the carbon skeleton.

• For example, "3,3-dimethyl" indicates two methyl groups are both attached to the third carbon.
• Methyl groups can alter a compound's molecular weight, boiling point, and reactivity depending on their position and quantity.

Understanding methyl substituents helps in predicting and rationalizing the behavior of more complex organic molecules, as they can sterically hinder reactions or create more stable conformations in cyclic structures.