Question 1

How can substitution, addition, elimination and rearrangement reactions be distinguished?

Accepted Answer

Substitution replaces one atom or group with another while the reacting saturated carbon usually retains four sigma bonds. Addition breaks a pi bond and forms new sigma bonds across it. Elimination removes two groups and creates a pi bond, while rearrangement transfers an atom or group to a different position within the same molecule.

Question 2

What happens during bromination of methane?

Accepted Answer

In suitable light, one hydrogen atom of methane is replaced by bromine. The products are bromomethane and hydrogen bromide: CH4 + Br2 gives CH3Br + HBr. The reaction is substitution and halogenation, not elimination.

Question 3

Why does ethene have trigonal-planar geometry?

Accepted Answer

Each carbon in a simple C=C bond is sp2-hybridized and has three regions of electron density. Its bond angles are therefore approximately 120 degrees. After hydrogenation to ethane, each carbon becomes sp3 and the tetrahedral angle is approximately 109.5 degrees.

Question 4

What leaves during dehydrohalogenation of bromoethane?

Accepted Answer

The leaving groups are bromine from the carbon bearing bromine and a hydrogen from the adjacent beta-carbon. Heating with alcoholic KOH produces ethene, KBr and water, and a new C=C bond forms between the two carbon atoms.

Question 5

Is rearrangement the same as substitution?

Accepted Answer

No. In substitution, one group is removed and another group takes its place. In rearrangement, an atom or group migrates from one position to another within the molecule, so no group is simply exchanged with an external reactant.

Organic Reaction Types: Substitution, Addition, Elimination and Rearrangement

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