Q.33 The degree of reduction for acetic acid (C₂H₄O₂) is __________.

The degree of reduction for acetic acid (C₂H₄O₂) is 4 per carbon atom, or a total of 8 for the molecule. This value quantifies the electrons available for transfer in oxidation reactions, crucial for biochemical and bioenergetic analyses. Calculations follow the standard formula γ = 4c + h – 2o, where c, h, and o are atoms of carbon, hydrogen, and oxygen.

Calculation Method

The formula for degree of reduction (γ) assigns valence electrons: +4 per C, +1 per H, and -2 per O (reflecting their oxidation states). For acetic acid (CH₃COOH or C₂H₄O₂):

γ = 4(2) + 4 – 2(2) = 8 + 4 – 4 = 8

Per carbon atom (common in biochemistry): 8 ÷ 2 = 4, matching carbohydrates like glucose. No options are provided in the query, but this rules out common errors like γ = 6 (ignoring O penalty) or γ = 12 (treating as hydrocarbon).

Formula and Step-by-Step Solution

Apply the standard degree of reduction formula:

γ = 4 × (number of C atoms) + 1 × (number of H atoms) − 2 × (number of O atoms)

For acetic acid (C₂H₄O₂):

• c = 2, h = 4, o = 2
• γ = 4(2) + 4 – 2(2) = 8 + 4 – 4 = 8

Per carbon-mole (biochemically standard): 8 ÷ 2 = 4, same as glucose (C₆H₁₂O₆: γ=24, 24/6=4) and lactic acid. This confirms acetic acid’s carbohydrate-like reduction state in glycolysis/fermentation.

Common Mistakes (Explaining “Options”)

Though no explicit options exist, exam traps include:

• Ignoring oxygen: 4(2)+4=12 (wrong, overestimates electrons).
• Using CO₂ reference wrongly: CO₂ has γ=0; acetic is partially reduced.
• Molecular vs. per C confusion: Total γ=8, but questions often expect 4.
• Formula mix-up: Some use γ=4+h-o (incorrect valence).

 answer: 8 (total) or 4 (per C, context-dependent).

Biochemical Relevance

In bioenergetics, γ=4 per C for acetic acid explains its role in acetogenesis and yield coefficients (Y_x/s). Compare:

This uniformity aids electron balance in redox reactions.