Organic Chemistry
8 marks · NormalThis question is about the IUPAC naming of alcohols and carboxylic acids.
State the IUPAC (systematic) name for the alcohol with structural formula CH3CH(OH)CH3.
Give the IUPAC (systematic) name for the carboxylic acid with the displayed formula:
Give the name and the correct IUPAC name for the alcohol with the formula CH3CH2CH2CH2OH.
State the name of the main component of vinegar.
Why does propanoic acid not require a number in its IUPAC name, while alcohols such as propanol often do?
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) propan-2-ol · must show propan-2-ol, or isopropanol (accept propan-2-ol as correct IUPAC)
(b) propanoic acid · must show propanoic acid
(c) butan-1-ol; butanol also accepted. · must show butan-1-ol; accept butanol
(d) ethanoic acid · must show ethanoic acid
(e) Because the –COOH group is always on the end carbon in carboxylic acids, its position does not need to be specified in the name. In alcohols, the –OH can be on different carbons, so a number is needed. · must show COOH always at end, –OH can be on different carbons
Also accept: propanol is acceptable for propan-1-ol and butanol for butan-1-ol where mentioned
Common mistakes: omitting numbers in alcohol names; confusing the acid and alcohol name stems
Show mark scheme and worked solution
Marking points
A1 (a) · 2 marks · propan-2-ol (must include number); allow isopropanol for 1 mark.
B1 (b) · 2 marks · propanoic acid only; do not accept propionic acid.
C1 (c) · 2 marks · 1 mark each for (i) butan-1-ol, (ii) butanol (accept both). If only one name, award 1 mark.
D1 (d) · 1 mark · ethanoic acid only.
E1 (e) · 1 mark · Must mention the carboxyl group always at end so no number needed, but alcohols can have the –OH on different positions.
Worked solution
a) The structure CH3CH(OH)CH3 is propan-2-ol, as the –OH is on the middle carbon of a three-carbon chain.
b) The displayed formula shows a three-carbon chain with a COOH group at the end: CH3–CH2–COOH. The systematic name is propanoic acid.
c) CH3CH2CH2CH2OH can be named as butan-1-ol (preferred IUPAC); butanol is also accepted.
d) The main component of vinegar is ethanoic acid.
e) In carboxylic acids, the COOH group is always at the end of the chain, so its position does not need to be specified; alcohols require a number because the –OH group can be on different carbons.