Question

Which are carcinogenic hydrocarbon
(i) 1,2 - Benzanthracene
(ii) pent-1-yne
(iii) 1,2 - Benpyrene
(iv) cyclohexane
(v) 3-methyl cholanthrene

Hint:

As a general rule in organic environmental chemistry, hydrocarbons with 3 or more fused aromatic rings (PAHs) should immediately be flagged as potentially carcinogenic and toxic.

Answer 1

Step 1: Understanding the Concept:
Carcinogenic hydrocarbons are toxic compounds capable of causing cancer in living tissues. They are typically Polynuclear Aromatic Hydrocarbons (PAHs) containing multiple fused benzene rings.
Step 2: Key Formula or Approach:
The approach is to identify which of the given compounds are complex, fused-ring aromatic structures known for their toxicity and carcinogenicity.
Step 3: Detailed Explanation:
Polynuclear aromatic hydrocarbons containing more than two benzene rings fused together are generally toxic and possess cancer-producing (carcinogenic) properties. They are formed during the incomplete combustion of organic materials like tobacco, coal, and petroleum.
Let's evaluate the options:
(i) 1,2-Benzanthracene: This is a well-known PAH consisting of four fused aromatic rings. It is highly carcinogenic.
(ii) Pent-1-yne: This is a simple aliphatic alkyne. It is not carcinogenic.
(iii) 1,2-Benpyrene (Benzopyrene): This is a five-ring PAH, famously found in coal tar and cigarette smoke, and is one of the most potent known carcinogens.
(iv) Cyclohexane: This is a simple non-aromatic cyclic alkane. It is relatively non-toxic and not carcinogenic.
(v) 3-methyl cholanthrene: This is a highly potent carcinogenic PAH widely used in laboratory research to induce tumors in study models.
Therefore, the carcinogenic hydrocarbons are (i), (iii), and (v).
Step 4: Final Answer:
(i) 1,2-Benzanthracene, (iii) 1,2-Benpyrene, and (v) 3-methyl cholanthrene are carcinogenic.