Test: Hydrocarbons (October 12) - NEET MCQ

The acidity of acetylene or 1--alkynes can be explained on the basis of molecular orbital concept according to which formation of C—H bond in acetylene involves sphybridised carbon atom. Now since s electrons are closer to the nucleus than p electrons, the electrons present in a bond having more s character will be correspondingly more closer to the nucleus.
Thus owing to high s character of the C—H bond in alkynes (s = 50%), the electrons constituting this bond are more strongly held by the carbon nucleus (i.e., the acetylenic carbon atom or the sp orbital acts as more electronegative species than the sp² and sp³ with the result the hydrogen  present on such a carbon atom (≡C—H) can be esily removed as a proton.

Benzene do not show addition reaction like other unsaturated hydrocarbons. However it show substitution reactions. Due to resonance all the C – C bonds have the same nature, which is possible because of the cycli c del oca lisati on of π-electr on s in benzene. Monosubstitution will give only a single product.

Reduction of alkynes with Na/liq. NH₃ gives trans-alkenes. This reaction is called Birch reduction

The reactivity of H-atoms depends upon the stability of free radicals follows the order : Tertiary > secondary > primary, therefore, reactivity of H-atoms follows the same order, i.e., tertiary > secondary > primary.

When 3, 3 dimethyl 2-butanol is heated with H₂SO₄ the major product obtained is 2, 3 dimethyl 2-butene.

We know that

Gasoline (petrol) is a mixture of alkanes, alkenes and aromatic hydrocarbons. The quality of a gasoline is determined by the amount of branched chain hydrocarbons (2,2,4-trimethylpentane, commonly known as iso-octane) present in it.

We know that

Temperature

While at 220º – 250ºC it forms ether