Which of the following statements is not true ? (a)...

Which of the following statements is not true ? (a) Acetylene is used in the preparation of butadiene. (b) Butyne $-1$ gives red precipitate with ammoniacal cuprous chloride but Butyne $-2$ will not (c) The number of sigma and pi- bonds in 1 - butene $-3$ - yne are 8 and 4 respectively (d) Propene when heated with chlorine at $500^{\circ} \mathrm{C}$ forms $\mathrm{CH}_{2} \mathrm{ClCH}=\mathrm{CH}_{2}$.

Which of the following statements is not true ?
(a) Acetylene is used in the preparation of butadiene.
(b) Butyne $-1$ gives red precipitate with ammoniacal cuprous chloride but Butyne $-2$ will not
(c) The number of sigma and pi- bonds in 1 - butene $-3$ - yne are 8 and 4 respectively
(d) Propene when heated with chlorine at $500^{\circ} \mathrm{C}$ forms $\mathrm{CH}_{2} \mathrm{ClCH}=\mathrm{CH}_{2}$.

Key Concepts

Organic Synthesis of Conjugated Dienes

This concept involves the formation of conjugated systems, such as dienes, from simpler unsaturated molecules. It focuses on the strategies and reaction mechanisms used to build larger and more reactive framework compounds from smaller alkynes or alkenes, highlighting the importance of precursor choice and reaction conditions in achieving the desired product synthesis.

Reactivity of Terminal versus Internal Alkynes

Terminal alkynes (those with an acidic hydrogen at the end of the triple bond) display distinct reactivity compared to internal alkynes, particularly in reactions involving metal-based reagents. Their sufficiently acidic hydrogen allows for specific interactions, such as forming complexes or precipitates with reagents like ammoniacal cuprous chloride, which is used as a qualitative test to differentiate between terminal and internal alkynes.

Halogenation Reaction Mechanisms

Halogenation reactions, especially in alkenes, entail the addition of halogen atoms under specific conditions, such as heat or light. This concept covers both the mechanism of free radical halogenations and electrophilic additions, emphasizing how reaction conditions (e.g., temperature and the presence of excess halogen) determine the regioselectivity and outcome of the halogenated products.

Sigma and Pi Bonding in Organic Molecules

Understanding the nature of sigma (?) and pi (?) bonds is crucial in organic chemistry because it influences molecular structure, reactivity, and properties. This concept involves counting and identifying the types of bonds present in a molecule, acknowledging that sigma bonds form the primary framework, while pi bonds, present in double and triple bonds, add to the degree of unsaturation and impact chemical reactivity.

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