Question

Differentiate between primary, secondary and tertiary alcohols, showing their structure. In the presence of which enzyme does glucose convert to ethyl alcohol? (3+1)

Hint:

Classify by the number of carbons bonded to the C-OH carbon (one, two, three). The yeast enzyme that ferments glucose to ethanol is zymase.

Answer 1

Step 1 (basis of classification): Count how many carbon atoms surround the C atom holding the hydroxyl. One, two or three neighbouring carbons make the alcohol primary, secondary or tertiary respectively.

Step 2 (primary): Structure \(R-CH_2-OH\); the carbinol carbon also carries two H atoms. Typical example is ethanol \(CH_3CH_2OH\); methanol \(CH_3OH\) is also grouped here.

Step 3 (secondary): Structure \(\begin{array}{c} R \\ | \\ R'-CH-OH \end{array}\), i.e. \(R_2CHOH\), one H on the carbinol carbon. Example propan-2-ol, \((CH_3)_2CHOH\).

Step 4 (tertiary): Structure \(R_3C-OH\), no H on the carbinol carbon. Example 2-methylpropan-2-ol, \((CH_3)_3COH\).

Step 5 (fermentation enzyme): In alcoholic fermentation the enzyme zymase (secreted by yeast) breaks glucose down into ethanol and carbon dioxide, \(C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2\).
\(\boxed{\text{zymase}}\)