Ch-12. Organic Chemistry : Some Basic Principles and Techniques (Exercise) Page 361

Question 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 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 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 4:	Give the IUPAC names of the following compounds: (a) (b) (c) (d) (e) (f) Cl2CHCH2OH
Answer :	(a) 3–phenyl propane (b) 2–methyl–1–cyanobutane (c) 2, 5–dimethyl heptane (d) 3–bromo–3–chloroheptane (e) 3–chloropropanal (f) Cl2CHCH2OH 1, 1–dichloro–2–ethanol
Question 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.