Chapter 8: Organic Chemistry – Some Basic Principles & Techniques

(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.

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

Isopropyl alcohol

2, 3–dimethyl butanal

Heptan–4–one

(a)

Propylbenzene

(b)

3–methylpentanenitrite

(c)

2,5–dimethyl heptane

(d)

3–bromo–3–chloroheptane

(e)

3–chloropropanal

(f) Cl₂CHCH₂OH

2,2–dichloroethanol

(a) The prefix di shows that there are two methyl groups in the chain. Thus, the correct IUPAC name would be 2,2-Dimethylpentane.

(b) The locant number should start from the minimum. Here, 2,4,7 is lower than 2,5,7. Thus, the correct IUPAC name would be 2,4,7-Trimethyloctane.

(c) If the substituents in the chain are in equivalent positions, then the lower number is given to the substituent group in alphabetical order. Thus, the correct IUPAC name would be 2-Chloro-4-methylpentane.

(d) Out of the two functional groups present in the given compound, the alcoholic group is the principal functional group. Thus, the parent chain will have an –ol suffix. Since the alkyne group is in C–3, the IUPAC name would be But–3–yn–1–ol.

The first five members of each homologous series beginning with the given compounds, are

(a)

H–COOH: Methanoic acid

CH₃–COOH: Ethanoic acid

CH₃–CH₂–COOH: Propanoic acid

CH₃–CH₂–CH₂–COOH: Butanoic acid

CH₃–CH₂–CH₂–CH₂–COOH: Pentanoic acid

(b)

CH₃COCH₃: Propanone

CH₃COCH₂CH₃: Butanone

CH₃COCH₂CH₂CH₃ : Pentan-2-one

CH₃COCH₂CH₂CH₂CH₃: Hexan-2-one

CH₃COCH₂CH₂CH₂CH₂CH₃ : Heptan-2-one

(c)

H–CH=CH₂: Ethene

CH₃–CH=CH₂: Propene

CH₃–CH₂–CH=CH₂: 1-Butene

CH₃–CH₂–CH₂–CH=CH₂: 1-Pentene

CH₃–CH₂–CH₂–CH₂–CH=CH₂: 1-Hexene

(a) 2, 2, 4–Trimethylpentane

Condensed formula

(CH₃)₂CHCH₂C (CH₃)₃

Bond line formula :

(b) 2–Hydroxy–1, 2, 3–propanetricarboxylic acid

Condensed formula

(COOH)CH₂C(OH) (COOH)CH₂(COOH)

Bond line formula:

Functional groups:

Carboxylic acid (-COOH) and Hydroxyl (-OH) groups

(c) Hexanedial

Condensed formula

(CHO)(CH₂)₄(CHO)

Bond line formula:

Functional groups:

Aldehyde (-CHO)

(a) Hydroxyl (–OH), Aldehyde (–CHO), Methoxy (–OMe),

C=C double bond

(b) Ester -(O = C – O)-, 1^oAmino (–NH₂) (aromatic), Diethylamine CH₂N(C₂H₅)₂ – 30 Amine group

(c) Nitro (–NO₂),

C=C Ethylenic double bond

Since NO₂ belongs to the electron-withdrawing group, it shows the –I effect. NO₂ tries to decrease the negative charge on the compound by withdrawing the electrons towards it. This stabilises the compound, whereas the ethyl group belongs to the electron-releasing group and shows the +I effect. This results in an increase in the negative charge on the compound, thus destabilising the compound. Hence, O₂NCH₂CH₂O^– is expected to be more stable than CH₃CH₂O^–.

Due to hyperconjugation, an alkyl group behaves as an electron-donor group when attached to a π system. For example, propane (see the figure above).

The sigma electrons of the C-H bond get delocalised due to hyperconjugation. The alkyl is attached directly to an unsaturated system. The delocalisation happens due to the partial overlap of an sp³-s sigma bond orbital with an empty p orbital of the n bond of an adjacent carbon atom.

This process can be shown as follows:

The overlap, as shown above, results in delocalisation, making the compounds more stable.