INTRODUCTION - Chapter 12 Organic Chemistry class 11 ncert solutions Chemistry - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Question 12.1:

What are hybridisation states of each carbon atom in the following compounds?

CH₂=C=O, CH₃CH=CH₂, (CH₃)₂CO, CH₂=CHCN, C₆H₆

Answer:

(i) 

C–1 is sp² hybridised.

C–2 is sp hybridised.

(ii) 

C–1 is sp³ hybridised.

C–2 is sp² hybridised.

C–3 is sp² hybridised.

(iii)

C–1 and C–3 are sp³ hybridised.

C–2 is sp² hybridised.

(iv) 

C–1 is sp² hybridised.

C–2 is sp² hybridised.

C–3 is sp hybridised.

(v) C₆H₆

All the 6 carbon atoms in benzene are sp² hybridised.

Question 12.2:

Indicate the σ and π bonds in the following molecules:

C₆H₆, C₆H₁₂, CH₂Cl₂, CH₂ = C = CH₂, CH₃NO₂, HCONHCH₃

Answer:

(i) C₆H₆

There are six C–C sigma ( ) bonds, six C–H sigma ( ) bonds, and three C=C pi ( ) resonating bonds in the given compound.

(ii) C₆H₁₂

There are six C–C sigma ( ) bonds and twelve C–H sigma ( ) bonds in the given compound.

(iii) CH₂Cl₂

There two C–H sigma ( ) bonds and two C–Cl sigma ( ) bonds in the given compound.

(iv) CH₂ = C = CH₂

There are two C–C sigma ( ) bonds, four C–H sigma ( ) bonds, and two C=C pi ( ) bonds in the given compound.

(v) CH₃NO₂

There are three C–H sigma ( ) bonds, one C–N sigma ( ) bond, one N–O sigma ( ) bond, and one N=O pi ( ) bond in the given compound.

(vi) HCONHCH₃

There are two C–N sigma ( ) bonds, four C–H sigma ( ) bonds, one N–H sigma bond, and one C=O pi ( ) bond in the given compound.

Question 12.3:

Write bond line formulas for: Isopropyl alcohol, 2,3-Dimethyl butanal, Heptan-4-one.

Answer:

The bond line formulae of the given compounds are:

(a) Isopropyl alcohol

(b) 2, 3–dimethyl butanal

(c) Heptan–4–one

Question 12.4:

Give the IUPAC names of the following compounds:

(a)

(b)

(c)

(d)

(e)

(f) Cl₂CHCH₂OH

Answer:

(a)

1–phenyl propane

(b)

3–methylpentanenitrile

(c)

2, 5–dimethyl heptane

(d)

3–bromo–3–chloroheptane

(e)

3–chloropropanal

(f) Cl₂CHCH₂OH

2,2- Dichloroethanol

Question 12.5:

Which of the following represents the correct IUPAC name for the compounds concerned? (a) 2,2-Dimethylpentane or 2-Dimethylpentane (b) 2,4,7-Trimethyloctane or 2,5,7-Trimethyloctane (c) 2-Chloro-4-methylpentane or 4-Chloro-2-methylpentane (d) But-3-yn-1-ol or But-4-ol-1-yne

Answer:

(a) The prefix di in the IUPAC name indicates that two identical substituent groups are present in the parent chain. Since two methyl groups are present in the C–2 of the parent chain of the given compound, the correct IPUAC name of the given compound is 2, 2–dimethylpentane.

(b) Locant number 2, 4, 7 is lower than 2, 5, 7. Hence, the IUPAC name of the given compound is 2, 4, 7–trimethyloctane.

(c) If the substituents are present in the equivalent position of the parent chain, then the lower number is given to the one that comes first in the name according to the alphabetical order. Hence, the correct IUPAC name of the given compound is 2–chloro–4–methylpentane.

(d) Two functional groups – alcoholic and alkyne – are present in the given compound. The principal functional group is the alcoholic group. Hence, the parent chain will be suffixed with ol. The alkyne group is present in the C–3 of the parent chain. Hence, the correct IUPAC name of the given compound is But–3–yn–1–ol.