Class 11th

(a) Here, HO^– acts as a nucleophile as it is an electron-rich species, i.e., it is a nucleus-seeking species.

(b) Here, –CN acts as a nucleophile as it is an electron-rich species, i.e., it is a nucleus-seeking species.

(c) CH₃C⁺O acts as an electrophile as it is an electron deficient species.

Electrophiles: The name electrophiles mean electron loving. Electrophiles are electron deficient. They may be positive ions or neutral molecules.
Ex: H⁺, Cl⁺, Br⁺, NO₂⁺, R₃C⁺, RN₂⁺, AlCl₃, BF₃
Nucleophiles: The name nucleophiles means 'nucleus loving' and indicates that it attacks the region of low electron density (positive centres) in a substrate molecule. They are electron rich they may be negative ions or neutral molecules.
Ex: Cl^– Br^–, CN^–, OH^–, RCR₂^–, NH₃, RNH₂, H₂O, ROH etc.

Due to hyperconjugation, alkyl groups act as electron donors when attached to a π - system as shown below:

Nitroethoxide ion (O₂NCH₂CH₂O^–) is more stable than ethoxide ion (CH₃CH₂O^–) due to -I effect of nitro group which decreases the negative charge of oxide ion of nitroethoxide ion leading to stability. In contrast, CH₃CH₂ has +I-effect. It, therefore, tends to intensify the -ve charge and hence destabilizes it.

4.29 (c) It will not form a sigma bond because taking x-axis as the inter-nuclear axis, there will be lateral overlap between the two 2p_y orbitals forming a -bond.

4.28.  (a) Acetylene C_2? H₂? contains 3? bonds and 2? bonds.

(b) Ethylene C_2? H₄? contains 5? bonds and 1? bond.

(a) H-COOH

CH₃—COOH
CH₃CH₂—COOH

CH₃CH₂CH₂—COOH
CH₃CH₂CH₂CH₂—COOH

(b) CH₃COCH₃
CH₃COCH₂CH₃
CH₃COCH₂CH₂CH₃
CH₃COCH₂CH₂CH₂CH₃
CH₃CO (CH₃)₄CH₃

(c) H—CH=CH₂
CH₃CH=CH₂

CH₃CH₂CH=CH₂
CH₃CH₂CH₂CH=CH₂
CH₃CH₂CH₂CH₂CH=CH₂

(a) 2, 2-Demethylpentane

(b) 2, 4, 7-Trimethyloctane. For two alkyl groups on the same carbon its locant is repeated twice, 2, 4, 7-locant set is lower than 2, 5, 7.
(c) 2- Chloro-4-methylpentane. Alphabetical order of substituents, (d) But-3-yn-1-ol. Lower locant for the principal functional group, i.e., alcohol.