Page 39 - Q & A STPM 2022 Chemistry

Chemistry Term 3 STPM Chapter 14 Introduction to Organic Chemistry
Question 4

Ibuprofen, a nonsteroid anti-inflammatory drug used for pain-relief has the
following structure.
CH 3
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COOH
CH 3
H 3 C

Which of the following is not correct regarding ibuprofen?
C It is insoluble in water.
A Its molecular formula is C 13 H 16 O 2 .
B It is a carboxylic acid. D It has one chiral centre.

Answer: A
The molecular formula is C 13 H 18 O 2 .
The !COOH is a carboxylic acid group.
The chiral centre is marked with an asterisk.

CH 3
* COOH
CH 3
H 3 C

The presence of large hydrophobic hydrocarbon groups makes it insoluble in
water.

14.7 Inductive and Resonance Effect

Section A Multiple-choice Questions

Question 1
Arrange the following compounds in the order of increasing K a values.
CH 3 COOH; ClCH 2 COOH; Cl 2 CHCOOH
I II III
A I, II, III B I, III, II C II, III, I D III, II, I

Answer: A
K a is a measure of the strength of an acid. The stronger the acid, the higher the Term
acid strength.
Chlorine is an electron-withdrawing group (negative inductive effect). It 3
weakens the O!H bond in the !COOH group thus increasing the acid
strength. The more chlorine there is the weaker the O!H bond.

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14 Q&A STPM Chem T3 Layout.indd 355 4/19/19 5:29 PM