Identify the correct IUPAC name of hydrocarbon (x) containing three primary carbon atoms and with molar mass 72 g mol-1.
- 1, 1 - Dimethylcyclopropane
- 2, 2 - Dimethylpropane
- 2 - Methylbutane
- n-pentane
Answer
(3) 2 - Methylbutane
Solution
An alkane CnH2n+2: 14n + 2 = 72 ⇒ n = 5 ⇒ C5H12
1,1-Dimethylcyclopropane is C5H10 (M = 70) ⇒ rejected.
Primary (1°) carbon = carbon attached to only one other carbon:
n-Pentane, CH3-CH2-CH2-CH2-CH3: two 1° carbons
2-Methylbutane, CH3- CH3 |CH-CH2-CH3: three 1° carbons
2,2-Dimethylpropane, C(CH3)4: four 1° carbons
∴ x = 2-Methylbutane
Answer: (3)