Basic Concepts of Organic Chemistry — A/L Chemistry

How do I practise Basic Concepts of Organic Chemistry?

1 question with a worked solution

Check before you answer: IUPAC Precedence & Numbering: Correct hierarchy of principal functional groups determining suffix priority and lowest locant numbering for substituents.

1. Which of the following organic compounds is capable of displaying both geometrical (cis-trans) isomerism and optical isomerism (enantiomerism)?
   1. A) 3-chloropent-2-ene
   2. B) 1-chlorobut-2-ene
   3. C) 2-chlorobut-2-ene
   4. D) 2-chloropent-3-ene
   Check my answer

   Correct answer: D) 2-chloropent-3-ene

   2-chloropent-3-ene has the structure CH₃-CH(Cl)-CH=CH-CH₃. Around the C3=C4 double bond, each sp² carbon is bonded to two different groups (C3 is bonded to -H and -CH(Cl)CH₃; C4 is bonded to -H and -CH₃), satisfying the criteria for geometrical (cis-trans) isomerism. Furthermore, C2 is bonded to four distinct groups (-H, -Cl, -CH₃, and -CH=CH-CH₃), making it an asymmetric/chiral carbon center that exhibits optical activity.

   Show worked solution

   Step 1: Check conditions for geometrical isomerism: restricted rotation around C=C and each alkene carbon must hold two non-identical groups. Step 2: Check conditions for optical isomerism: presence of at least one sp³ carbon bonded to 4 completely different substituents. Step 3: Analyze 2-chloropent-3-ene: CH₃-C*H(Cl)-CH=CH-CH₃: - C3 has -H and -CH(Cl)CH₃ (different) - C4 has -H and -CH₃ (different) → shows cis and trans isomers. - C2 (*) has -H, -Cl, -CH₃, -CH=CH-CH₃ (4 different groups) → chiral center (enantiomers). Step 4: Other choices fail: 1-chlorobut-2-ene has no chiral center; 2-chlorobut-2-ene has no chiral center. Answer: 2-chloropent-3-ene.
   Modelled on: the A/L Chemistry examination pattern

Get this auto-marked

Next in the syllabus

Where does Basic Concepts of Organic Chemistry fit in the syllabus?

Grade 12 · Term 3