Practice MCQs for JEE Chemistry Organic Chemistry Some Basic Principles and Techniques
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Multiple Choice Questions
(a) 4-Methyl-5-chloro-nitrobenzene
(b) 2-Chloro-1-methyl-4-nitrobenzene
(c) 1-Chloro-2-methyl-5-nitrobenzene
(d) 1-Methyl-2-chloro-4-nitrobenzene
Show Answer & Explanation
Answer: (b) 2-Chloro-1-methyl-4-nitrobenzene
Explanation:
1. The ring carries CH3, Cl (next to CH3) and NO2 (opposite to CH3).
2. All three are prefixes, so number to get the lowest set of locants. Giving CH3 = 1, Cl = 2, NO2 = 4 gives the set {1, 2, 4}, the lowest possible.
3. Write the prefixes alphabetically: chloro, methyl, nitro. Name: 2-chloro-1-methyl-4-nitrobenzene.
Teacher's Note:
1. Substituents on benzene are cited alphabetically, not in order of locants. Number first for the lowest locant set, and only use alphabetical order to break a tie.
(a) Hex-1-en-5-yn-4-ol
(b) Hex-5-en-1-yn-3-ol
(c) 4-Hydroxyhex-1-en-5-yne
(d) 3-Hydroxyhex-5-en-1-yne
Show Answer & Explanation
Answer: (b) Hex-5-en-1-yn-3-ol
Explanation:
1. The main chain has 6 carbons and contains the OH group, one double bond and one triple bond.
2. The suffix -ol is the principal group, so it must get the lowest locant. Numbering from the alkyne end puts OH on C3 (from the other end it would be C4).
3. That numbering gives the triple bond C1 and the double bond C5. Name: hex-5-en-1-yn-3-ol.
Teacher's Note:
1. The principal functional group (here -OH) decides the numbering direction first. Multiple bonds come next, and in the name the ene is written before the yne.
(a) 3-Ethyl-4-isopropylhex-1-ene
(b) 3,4-Diisopropylhex-1-ene
(c) 4-Ethyl-3-isopropyl-5-methylhex-1-ene
(d) 3-Ethyl-4-isopropyl-2-methylhex-5-ene
Show Answer & Explanation
Answer: (c) 4-Ethyl-3-isopropyl-5-methylhex-1-ene
Explanation:
1. The structure is CH2=CH–CH[CH(CH3)2]–CH[CH(CH3)2]–CH2CH3.
2. Several chains of 6 carbons containing the double bond are possible. Choose the one that carries the greatest number of substituents: C1=C2–C3–C4–C5(H)(CH3)–C6 passes through one isopropyl group, leaving an isopropyl at C3, an ethyl at C4 and a methyl at C5 (three substituents).
3. Name alphabetically: 4-ethyl-3-isopropyl-5-methylhex-1-ene.
Teacher's Note:
1. When two chains have the same length, pick the one with more substituents. Always number so the double bond gets the lowest locant.
(a) 3-Hydroxybutane-1,3,5-trioic acid
(b) 3-Hydroxy-4-carboxyhexane-1,6-dioic acid
(c) 2-Hydroxybutane-1,3,4-tricarboxylic acid
(d) 3-Hydroxybutane-1,2,4-tricarboxylic acid
Show Answer & Explanation
Answer: (d) 3-Hydroxybutane-1,2,4-tricarboxylic acid
Explanation:
1. Choose as parent the chain that carries the largest number of the principal group (COOH). The chain C(a)–C(OH)–C(b)–C(c) is a butane that bears three COOH groups, one on each of three carbons, so they are named as -tricarboxylic acid.
2. Number from the end that gives the COOH carbons the lowest locants: the three COOH are on C1, C2 and C4 (the other direction gives 1, 3, 4).
3. The OH group is then on C3. Name: 3-hydroxybutane-1,2,4-tricarboxylic acid.
Teacher's Note:
1. Carboxylic acid carbons that are not part of the parent chain are named with the suffix -carboxylic acid. Count the principal groups first when choosing the parent chain.
(a) 3-Chloro-5-ethyl-5-methylcyclohex-1-ene
(b) 2-Chloro-4-ethyl-5-methylcyclohexene
(c) 6-Chloro-4-ethyl-3-methylcyclohex-1-ene
(d) 5-Chloro-3-ethyl-2-methylcyclohex-1-ene
Show Answer & Explanation
Answer: (c) 6-Chloro-4-ethyl-3-methylcyclohex-1-ene
Explanation:
1. The ring has one double bond, so the double-bond carbons are C1 and C2. There are two ways to number the ring; choose the one giving the lowest locant set to the substituents.
2. Going one way the substituents (Cl, Et, Me) are at 3, 5, 6; going the other way they are at 6, 4, 3, that is the set {3, 4, 6}, which is lower.
3. Alphabetical order: chloro, ethyl, methyl. Name: 6-chloro-4-ethyl-3-methylcyclohex-1-ene.
Teacher's Note:
1. In a cycloalkene the double bond fixes locants 1 and 2. The remaining choice of direction is settled by the lowest locant set of substituents.
(a) Phenyl o-hydroxybenzoate
(b) 3-Phenoxycarbonylphenol
(c) Phenyl 3-hydroxybenzoate
(d) None of these
Show Answer & Explanation
Answer: (c) Phenyl 3-hydroxybenzoate
Explanation:
1. The compound is an ester of benzoic acid with phenol. The ester is the principal group, so it is named as an alkyl (aryl) alkanoate: phenyl ... benzoate.
2. The OH group on the acid part is a substituent at position 3 relative to the carbonyl carbon (the C=O carbon is on C1).
3. Name: phenyl 3-hydroxybenzoate. The ortho isomer would put OH next to the ester group, which is not the case here.
Teacher's Note:
1. In an ester the group on oxygen is named first as a separate word, then the acid part ends in -oate. An OH on the acid part is only a hydroxy prefix.
(a) Tris(trichloromethyl)-1-chloromethane
(b) 2-Chloro-2-tris(chloromethyl)propane
(c) 1,1,1,2,3,3,3-Heptachloro-2-(trichloromethyl)propane
(d) 1,1,1-Trichloromethyl-1-chloromethane
Show Answer & Explanation
Answer: (c) 1,1,1,2,3,3,3-Heptachloro-2-(trichloromethyl)propane
Explanation:
1. The central carbon carries one Cl and three CCl3 groups.
2. Take the longest chain: CCl3–C(Cl)–CCl3, a propane. The third CCl3 is a trichloromethyl substituent on C2.
3. Chlorines on the chain: C1 has 3, C2 has 1, C3 has 3, so 1,1,1,2,3,3,3-heptachloro. Name: 1,1,1,2,3,3,3-heptachloro-2-(trichloromethyl)propane.
Teacher's Note:
1. A substituent that is itself substituted is named in brackets, for example (trichloromethyl). Count every halogen on the main chain in the locant list.
(a) Ethyl phenyl methanone
(b) 1-Phenylpropan-1-one
(c) 3-Phenylpropanone
(d) None of these
Show Answer & Explanation
Answer: (b) 1-Phenylpropan-1-one
Explanation:
1. The compound is a ketone: a C=O joined to a phenyl group and an ethyl group.
2. The longest chain containing C=O is 3 carbons (propane). The carbonyl is on C1, which also bears the phenyl group.
3. Name: 1-phenylpropan-1-one. (It is also called propiophenone.)
Teacher's Note:
1. For an aromatic ketone, the chain that carries the C=O is the parent and the benzene ring is a phenyl substituent. The name 'ethyl phenyl methanone' is not a valid systematic name.
(a) Diethyl dimethyl methane
(b) 2-Ethyl-2-methylbutane
(c) 3,3-Dimethylpentane
(d) None of these
Show Answer & Explanation
Answer: (c) 3,3-Dimethylpentane
Explanation:
1. Expand the formula: CH3CH2–C(CH3)2–CH2CH3.
2. The longest chain has 5 carbons (pentane) and the two methyl groups are on the middle carbon, C3.
3. Name: 3,3-dimethylpentane. (2-Ethyl-2-methylbutane would imply a longer chain exists, but the chain through both ethyl groups is longer.)
Teacher's Note:
1. Always look for the longest chain through the quaternary carbon, using the ethyl groups as part of it. Then number to give the lowest locants to substituents.
(a) 2-Propynylbuta-1,2-diene
(b) 4-Methylenehex-5-en-1-yne
(c) 3-Methylenehex-1-en-5-yne
(d) 2-Vinylpent-1-en-4-yne
Show Answer & Explanation
Answer: (c) 3-Methylenehex-1-en-5-yne
Explanation:
1. The structure is CH2=CH–C(=CH2)–CH2–C≡CH.
2. The longest chain containing both the double and the triple bond has 6 carbons, with the =CH2 group as a substituent (methylene).
3. Number to give the multiple bonds the lowest locants. Both directions give {1, 5}, so the double bond (ene) gets the lower number: C1=C2, C5≡C6.
4. Name: 3-methylenehex-1-en-5-yne.
Teacher's Note:
1. The longest chain is chosen first. Among equal numberings, the double bond gets the lower locant than the triple bond.
(a) 4-Cyanohexan-2-one
(b) 2-Ethyl-4-oxopentanenitrile
(c) 2-Oxo-4-cyanohexane
(d) 2-Oxohexane-4-nitrile
Show Answer & Explanation
Answer: (b) 2-Ethyl-4-oxopentanenitrile
Explanation:
1. Order of seniority: nitrile is senior to ketone, so the nitrile carbon is C1 of the parent chain and the ketone becomes an oxo prefix.
2. The longest chain including the nitrile carbon: C1 (CN carbon), C2 (CH), C3 (CH2), C4 (C=O), C5 (CH3), which is 5 carbons. The ethyl group on C2 is a substituent.
3. Name: 2-ethyl-4-oxopentanenitrile.
Teacher's Note:
1. The seniority order of groups matters: acids, esters, amides, nitriles, aldehydes, ketones, alcohols. The senior group is the suffix and the others become prefixes.
(a) Chloromethyl 3-methyl-2-oxobutanoate
(b) 1-Chloromethoxy-3-methylbutane-1,2-dione
(c) 2-Methyl-3-oxo-1-chloromethylbutanoate
(d) None of these
Show Answer & Explanation
Answer: (a) Chloromethyl 3-methyl-2-oxobutanoate
Explanation:
1. The compound is an ester: the group on oxygen is chloromethyl (CH2Cl).
2. The acid part is a 4-carbon chain: C1 is the ester carbon, C2 is the ketone C=O (oxo) and C3 carries a methyl, so it is a butanoate.
3. Prefixes in alphabetical order: methyl, then oxo. Name: chloromethyl 3-methyl-2-oxobutanoate.
Teacher's Note:
1. In an ester name the alkyl group on oxygen comes first as a separate word. Substituent prefixes on the acid part are written in alphabetical order.
(a) Hex-2-en-5-yne
(b) Hex-5-yn-2-ene
(c) Hex-4-en-1-yne
(d) Hex-1-yn-4-ene
Show Answer & Explanation
Answer: (c) Hex-4-en-1-yne
Explanation:
1. The chain has 6 carbons with one double and one triple bond.
2. Numbering from the triple-bond end gives the locants {1, 4}; numbering from the other end gives {2, 5}. The set {1, 4} is lower.
3. In the name the ene is written before the yne: hex-4-en-1-yne.
Teacher's Note:
1. Lowest locants go to all multiple bonds together first. Only when there is a tie does the double bond get the lower number. The name always lists ene before yne.
(a) 1,3-Dimethylhex-4-en-1-ol
(b) 4,6-Dimethylhex-2-en-6-ol
(c) 4-Methylhept-2-en-6-ol
(d) 4-Methylhept-5-en-2-ol
Show Answer & Explanation
Answer: (d) 4-Methylhept-5-en-2-ol
Explanation:
1. Expand the skeleton: CH3–CH=CH–CH(CH3)–CH2–CH(OH)–CH3. The main chain has 7 carbons.
2. OH is the principal group, so it gets the lowest locant: counting from the OH-end, the OH is on C2, the methyl on C4 and the double bond on C5.
3. Name: 4-methylhept-5-en-2-ol.
Teacher's Note:
1. The -ol suffix has priority over the double bond when numbering. A name such as hept-2-en-6-ol is wrong because it gives the OH a high locant.
(a) 3-Bromo-2-chloropentane
(b) Pent-2-en-4-yne
(c) 3-Bromobutan-2-ol
(d) 1-Aminopentane-2-thiol
Show Answer & Explanation
Answer: (b) Pent-2-en-4-yne
Explanation:
1. Pent-2-en-4-yne: numbering from the other end gives the multiple bonds the locants {1, 3}, which is lower than {2, 4}. The correct name is pent-3-en-1-yne.
2. 3-Bromo-2-chloropentane: halogens are prefixes, the locants {2, 3} are the lowest and the prefixes are alphabetical, so it is correct.
3. 3-Bromobutan-2-ol: OH gets the lowest locant, so it is correct.
4. 1-Aminopentane-2-thiol: the thiol (-SH) is senior to the amine, so thiol is the suffix and amino is a prefix, which is correct.
Teacher's Note:
1. Check each name for lowest locants and the correct choice of suffix. The locants of double and triple bonds are compared together as one set.
(a) 4
(b) 5
(c) 6
(d) 3
Show Answer & Explanation
Answer: (b) 5
Explanation:
1. The principal group is COOH, so the parent chain must include that carbon.
2. Chains that include the double bond are preferred: C1 (COOH), C2 (carbon bearing the CH2CH3 and COOH), C3 (=C bearing CHO), then CH2 and CH3 of the ethyl group on C3.
3. That chain has 5 carbons: it is 2-ethyl-3-formylpent-2-enoic acid. Choosing the ethyl on C2 would give only 4 carbons and no double bond in the chain.
Teacher's Note:
1. The parent chain must contain the principal group and, among chains that do, the multiple bond. Then the longer chain is chosen. A shorter chain that misses the double bond is not allowed.
(a) 2-Bromo-3-chloro-5,5-dimethylcyclohex-1-ene
(b) 1-Bromo-6-chloro-4,4-dimethylcyclohex-1-ene
(c) 4-Bromo-5-chloro-1,1-dimethylcyclohex-1-ene
(d) 1-Bromo-2-chloro-4,4-dimethylcyclohex-1-ene
Show Answer & Explanation
Answer: (b) 1-Bromo-6-chloro-4,4-dimethylcyclohex-1-ene
Explanation:
1. The double bond is between the C bearing Br and the neighbouring CH, so these are C1 and C2. Br is on C1 if we number towards the CH.
2. Numbering this way gives the substituent locants {1, 4, 4, 6} (Br 1, Me 4,4, Cl 6). The other way gives {2, 3, 5, 5}. The first set is lower at the first point of difference (1 against 2).
3. Name: 1-bromo-6-chloro-4,4-dimethylcyclohex-1-ene.
Teacher's Note:
1. After the double bond is fixed at C1=C2, compare the full locant sets of all substituents and take the set that is lower at the first difference.
(a) 4-Methylpentyl
(b) 1,3-Dimethylbutyl
(c) 2,4-Dimethylbutyl
(d) 3-Methylpentyl
Show Answer & Explanation
Answer: (b) 1,3-Dimethylbutyl
Explanation:
1. In a substituent group name, carbon 1 is the carbon bearing the free valence.
2. From C1 the longest chain is C1–C2H2–C3H(CH3)–C4H3, which is a butyl chain.
3. There is a methyl on C1 (the carbon with the free valence) and a methyl on C3. Name: 1,3-dimethylbutyl.
Teacher's Note:
1. The attachment point is always numbered 1 in a substituent name. Do not renumber from the other end as you would for a parent chain.
(a) Propylene oxide
(b) 1,2-Oxopropane
(c) 1,2-Epoxypropane
(d) 1,2-Propoxide
Show Answer & Explanation
Answer: (c) 1,2-Epoxypropane
Explanation:
1. The compound has a three-membered ring containing one oxygen: CH2–CH(CH3)–O.
2. Among the choices, the systematic substitutive-style name treats the oxygen bridge as an epoxy prefix on propane: 1,2-epoxypropane.
3. Propylene oxide is a common name, and the other two are not valid names.
Teacher's Note:
1. Epoxides are named by the prefix 'epoxy' with the two carbon locants (or as oxiranes). Common names such as propylene oxide are not IUPAC names.
(a) N-Formylaminoethane
(b) N-Ethylformylamine
(c) N-Ethylmethanamide
(d) Ethylaminomethanal
Show Answer & Explanation
Answer: (c) N-Ethylmethanamide
Explanation:
1. The compound is an amide: the carbonyl carbon is a one-carbon acyl group (HCO–) bonded to nitrogen.
2. The parent is methanamide (formamide). The ethyl group is on nitrogen, so its locant is N.
3. Name: N-ethylmethanamide.
Teacher's Note:
1. Substituents on the nitrogen of an amide get the locant N. Amide is senior to amine and aldehyde, so it decides the suffix.
(a) Tricarboxymethane
(b) Propanetrioic acid
(c) Tributanoic acid
(d) Methanetricarboxylic acid
Show Answer & Explanation
Answer: (d) Methanetricarboxylic acid
Explanation:
1. A single carbon bears three COOH groups. A chain of three carbons cannot give three -oic acid groups, since the middle carbon is not a terminal acid carbon.
2. So the parent is methane and the three COOH groups are named with the suffix -tricarboxylic acid.
3. Name: methanetricarboxylic acid.
Teacher's Note:
1. When COOH groups are attached to a chain carbon that is not at the chain end, the suffix is -carboxylic acid on the parent hydrocarbon.
(a) 4-Methylcyclopent-1-en-2-ol
(b) 2-Methylcyclopent-4-en-1-ol
(c) 3-Methylcyclopent-1-en-2-ol
(d) 5-Methylcyclopent-2-en-1-ol
Show Answer & Explanation
Answer: (d) 5-Methylcyclopent-2-en-1-ol
Explanation:
1. OH is the principal group, so the carbon bearing OH is C1.
2. Number in the direction that gives the double bond the lower locant: the double bond is then between C2 and C3.
3. The methyl group is on C5 (the other carbon next to C1). Name: 5-methylcyclopent-2-en-1-ol.
Teacher's Note:
1. In a ring with a suffix group, the suffix carbon is C1. Then the double bond decides the direction of numbering.
(a) 3-Aldo-2-oxopropanoic acid
(b) 2,3-Dioxopropanoic acid
(c) 1-Hydroxypropane-1,2,3-trione
(d) 2-Aldo-2-ketomethanoic acid
Show Answer & Explanation
Answer: (b) 2,3-Dioxopropanoic acid
Explanation:
1. The principal group is COOH, so the parent is propanoic acid: C1 is the COOH carbon.
2. C2 is a ketone carbonyl (an oxo group) and C3 is an aldehyde carbon, which is named as oxo when it is not the principal group.
3. Name: 2,3-dioxopropanoic acid.
Teacher's Note:
1. Aldo and keto are not IUPAC prefixes. A carbonyl that is not the principal group is always called oxo.
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