Page 32 - Q & A STPM 2022 Chemistry

Chemistry Term 3 STPM Chapter 14 Introduction to Organic Chemistry
Question 2

The following compound is used to treat skin problems. How many chiral
centres does it have?
O
H H C HO OH
3
HO
H C H
3
H H
O
A 3 C 7 OHRights Reserved.
B 5 D 8

Answer: C
Penerbitan Pelangi Sdn Bhd. All
HO O
18
HO 11 12 17 20 21
1 19 9 13 16
2 14
10 H 8 15
O 3 4 5 6 7

The chiral centes are at C-8, C-9, C-10, C-11, C-13, C-14 and C-17.

Section B Structured Questions
Question 3
(a) What do you understand by structural isomerism? Draw all the possible
structural isomers for chlorobutane, C 4 H 9 Cl and give their IUPAC names.
(b) Which of the above isomers is/are optically active? Mark the chiral centres
with an asterisk (*).

Answer:
(a) Structural isomerism refers to the occurrence of two or more compounds
having the same molecular formula but with different connectivity of
their atoms.
Term
CH 3CH 2 CH 2 CH 2Cl 1-Chlorobutane
3 CH 3 CH 2 !CH!CH 3 2-Chlorobutane
&
Cl

348

14 Q&A STPM Chem T3 Layout.indd 348 4/19/19 5:29 PM