Question

Draw structural formulas for each of the following alcohols. Indicate whether the alcohol is primary, secondary, or tertiary. a. 1 -butanol c. 2 -methyl-1-butanol b. 2 -butanol d. 2-methyl-2-butanol

Short answer

a. 1-butanol: CH3-CH2-CH2-CH2-OH (Primary) b. 2-butanol: CH3-CH(OH)-CH2-CH3 (Secondary) c. 2 -methyl-1-butanol: CH3-CH2-CH(CH3)-CH2-OH (Primary) d. 2-methyl-2-butanol: CH3-CH(OH)-CH(CH3)-CH3 (Tertiary)

Step-by-step solution

a. 1 -butanol

1-butanol is an alcohol with four carbon atoms. It has the molecular formula C4H9OH. The structure can be drawn as follows: CH3-CH2-CH2-CH2-OH 1-butanol is a primary alcohol because the hydroxyl group (OH) is attached to a carbon that is bonded to only one other carbon.

b. 2 -butanol

2-butanol is an alcohol with four carbon atoms. It has a molecular formula C4H9OH. The structure can be drawn as follows: CH3-CH(OH)-CH2-CH3 2-butanol is a secondary alcohol because the hydroxyl group (OH) is attached to a carbon that is bonded to two other carbon atoms.

c. 2 -methyl-1-butanol

2-methyl-1-butanol is an alcohol with five carbon atoms. It has the molecular formula C5H12O. The structure can be drawn as follows: CH3-CH2-CH(CH3)-CH2-OH 2-methyl-1-butanol is a primary alcohol because the hydroxyl group (OH) is attached to a carbon that is bonded to only one other carbon atom.

d. 2-methyl-2-butanol

2-methyl-2-butanol is an alcohol with five carbon atoms. It has the molecular formula C5H12O. The structure can be drawn as follows: CH3-CH(OH)-CH(CH3)-CH3 2-methyl-2-butanol is a tertiary alcohol because the hydroxyl group (OH) is attached to a carbon that is bonded to three other carbon atoms.

Key concepts

Primary Alcohol

Primary alcohols are a type of alcohol where the hydroxyl group (OH) is attached to a carbon atom that is bonded to only one other carbon atom. This is a very defining characteristic and is what distinguishes primary alcohols from other alcohols.

• The simplest example is methanol, where the carbon is bonded only to hydrogen atoms.
• Primary alcohols typically have the general formula R-CH2OH, where R is a substituent group.

In the examples provided in the exercise, two primary alcohols were discussed:

• 1-butanol: Here, the OH group is connected to an end carbon of the chain, which bonds with only one other carbon (R-CH2OH).
• 2-methyl-1-butanol: Similar to 1-butanol, the OH group is on a terminal carbon, thus classifying it as primary.

Thus, the presence of a primary alcohol heavily depends on the position of the OH group in relation to the entire carbon chain.

Secondary Alcohol

Secondary alcohols feature the hydroxyl group (OH) attached to a carbon atom, which is, in turn, bonded to two other carbon atoms. This setup clearly differentiates secondary alcohols from their primary counterparts.

• A classic example of a secondary alcohol is isopropanol, widely used as a disinfectant.
• Secondary alcohols have the general formula R2CHOH, meaning two substituent groups are connected to the carbon with the OH group.

In the given exercise:

• 2-butanol: This alcohol displays typical secondary structure, with the OH group attached to a central carbon connected to two other carbons forming a part of the backbone chain.

The nature of secondary alcohols lies in their unique structural position, making understanding them crucial for organic chemistry.

Tertiary Alcohol

Tertiary alcohols represent a further complexity where the hydroxyl-bearing carbon atom is bonded to three other carbon atoms. This distinct arrangement separates tertiary alcohols from both primary and secondary types.

• They do not easily oxidize, a notable characteristic due to the lack of hydrogen atoms bonded to the OH-bearing carbon.
• The general formula for tertiary alcohols is R3COH, with three substituent groups.

For instance, in the exercise, we have:

• 2-methyl-2-butanol: The OH group in this structure is bonded to a carbon centrally located among three other carbons, clearly categorizing it as a tertiary alcohol.

Understanding the sophisticated bonding and the placement of functional groups in tertiary alcohols helps students highlight the diversity and implications of carbon connectivity in organic structures.