Some Basic Principles and Techniques — NEET Chemistry MCQs with answers

Some Basic Principles and Techniques is a Class 11 Chemistry chapter in the NEET (UG) syllabus. NEET720 has 295 reviewed practice questions on it, each with a quick answer and a step-by-step explanation. The 8 questions below are free and fixed, so you can bookmark this page; the full chapter, plus mistake tracking and spaced revision, is in the app.

Topics covered

IUPAC nomenclature · Isomerism · Electronic effects · Reaction intermediates and stability · Bond fission and reaction types · Inductive effect · Hyperconjugation · Resonance effect · Aromaticity

8 free Some Basic Principles and Techniques practice questions with answers

Choose an answer in your head before opening it. Each explanation says why the correct option is right and, where relevant, why the tempting wrong option is wrong.

1. Question 1 · medium · IUPAC nomenclature

   A substituted heptane can be numbered from either end of its parent chain. One direction gives the substituent locant set {2, 3, 6} and the opposite direction gives {2, 4, 5}. Which set must be used in the IUPAC name?

   • A.{2, 4, 5}, because the largest individual locant (5) is smaller than the largest locant of the other set (6)
   • B.{2, 4, 5}, because its locants add up to a smaller total than {2, 3, 6}
   • C.{2, 3, 6}, because when locant sets are compared term by term at the first point of difference, 3 is lower than 4
   • D.Either set may be used, because the two sets have identical sums and IUPAC leaves such ties to the writer
   Show answer and explanation

   Answer: C. {2, 3, 6}, because when locant sets are compared term by term at the first point of difference, 3 is lower than 4

   Both sets total 11, so the sum is useless here. IUPAC compares the sets term by term after arranging each in increasing order: 2 = 2, then 3 < 4, so {2, 3, 6} wins at the first point of difference.

   The modern IUPAC rule is the 'rule of first point of difference', not a 'lowest sum' rule (the sum rule is only a shortcut that happens to agree in simple cases). Arrange each candidate set in increasing order and compare position by position: {2, 3, 6} versus {2, 4, 5}. The first terms tie at 2. The second terms are 3 and 4; since 3 < 4, the set {2, 3, 6} is lower and that numbering direction must be used, even though its last member (6) is larger. Option A invents a rule about the highest locant. Option B relies on the sum rule and additionally gets the arithmetic wrong, since 2+3+6 = 11 and 2+4+5 = 11 are equal. Option D wrongly concludes the rules permit a free choice.

   Common mistake: Treating 'lowest sum of locants' as the governing rule and giving up when the sums are equal

   Key point: When two numbering directions give locant sets of equal sum, compare them term by term from the lowest; the first place they differ decides.

2. Question 2 · medium · IUPAC nomenclature

   A branched alkane carries an isopropyl group and a tert-butyl group as substituents. When the prefixes are cited in alphabetical order in the name, how are these two names alphabetised?

   • A.Isopropyl is alphabetised under 'i' but tert-butyl is alphabetised under 'b', because the italicised structural prefix tert- is ignored for alphabetisation while iso- is an integral part of the substituent name
   • B.Both are alphabetised under 'b', since iso- and tert- are both ignorable structural prefixes
   • C.Isopropyl is alphabetised under 'p' (for propyl) and tert-butyl under 'b' (for butyl), since only the root alkyl name is ever used
   • D.Both are alphabetised under 't' and 'i' exactly as written, because IUPAC alphabetises on the first printed letter without exception
   Show answer and explanation

   Answer: A. Isopropyl is alphabetised under 'i' but tert-butyl is alphabetised under 'b', because the italicised structural prefix tert- is ignored for alphabetisation while iso- is an integral part of the substituent name

   Italicised prefixes such as tert-, sec-, n- and N- are ignored when alphabetising, so tert-butyl files under 'b'. The prefix iso- is not italicised and is part of the name, so isopropyl files under 'i'.

   Alphanumerical ordering of prefixes uses the first point of difference of the complete substituent prefix name, but italicised (structural or positional) prefixes are not counted: tert-, sec-, n-, N-, O-, o-, m- and p- are all skipped. So tert-butyl is alphabetised at 'butyl'. The contracted prefixes iso- and neo-, however, are written in roman type and are inseparable parts of the substituent name, so isopropyl is alphabetised at 'i' and neopentyl at 'n'. Consequently isopropyl (i) is cited after tert-butyl (b). Multiplying prefixes such as di- and tri- are likewise ignored, but that is a separate rule and does not apply to either name here.

   Common mistake: Treating iso- exactly like tert- and filing isopropyl under 'p'

   Key point: Ignore italicised prefixes (tert-, sec-, n-, N-) when alphabetising, but never ignore iso- or neo-.

3. Question 3 · medium · IUPAC nomenclature

   A propane skeleton carries two -CH2Cl (chloromethyl) groups on the same central carbon. Which multiplying prefix is correct for citing these two identical composite substituents, and why?

   • A.di-, written as 2,2-dichloromethylpropane, because di- is the normal prefix for two identical groups
   • B.No multiplying prefix at all; each chloromethyl group must be cited separately as '2-chloromethyl-2-chloromethyl'
   • C.tri-, because the composite substituent contains more than one atom type and composite substituents always take the next higher multiplying prefix
   • D.bis-, written as 2,2-bis(chloromethyl)propane, because the substituent name is itself composite and enclosing marks plus the bis/tris series are used to avoid ambiguity
   Show answer and explanation

   Answer: D. bis-, written as 2,2-bis(chloromethyl)propane, because the substituent name is itself composite and enclosing marks plus the bis/tris series are used to avoid ambiguity

   For composite (substituted) substituent prefixes, IUPAC uses bis-, tris-, tetrakis- with the substituent name in enclosing marks: 2,2-bis(chloromethyl)propane.

   The simple multiplying prefixes di-, tri-, tetra- are used for simple substituents (dimethyl, trichloro). When the substituent is itself substituted or composite, using di- can be read ambiguously: '2,2-dichloromethylpropane' would naturally be parsed as two chloro atoms and a methyl group. IUPAC therefore prescribes the alternative series bis-, tris-, tetrakis-, combined with enclosing marks around the composite substituent name, giving 2,2-bis(chloromethyl)propane. The same convention gives names such as tris(hydroxymethyl) and bis(dimethylamino). Option A produces the ambiguous name; option B abandons contraction, which IUPAC never does; option C invents a count-shifting rule.

   Common mistake: Writing dichloromethyl instead of bis(chloromethyl), which changes the structure implied by the name

   Key point: Composite substituent names take bis-, tris-, tetrakis- with enclosing marks; simple substituents take di-, tri-, tetra-.

4. Question 4 · medium · IUPAC nomenclature

   Cyclohexane bearing one -CHO group directly on the ring is named cyclohexanecarbaldehyde, whereas the open-chain compound CH3-CH2-CHO is named propanal. What justifies the different suffix treatment?

   • A.Ring aldehydes are named with -carbaldehyde because the -CHO carbon is less reactive than a chain -CHO carbon and therefore ranks lower in seniority
   • B.In propanal the -CHO carbon is counted as C1 of the parent chain, but a ring cannot be opened to absorb the -CHO carbon, so the suffix -carbaldehyde is used to name a -CHO carbon that lies outside the parent ring
   • C.Because cyclohexane has six carbons, the aldehyde must be named as a seven-carbon chain, heptanal, and carbaldehyde is only an accepted trivial alternative
   • D.Cyclohexanecarbaldehyde uses the suffix -carbaldehyde only because cyclohexanal would be confused with cyclohexanol
   Show answer and explanation

   Answer: B. In propanal the -CHO carbon is counted as C1 of the parent chain, but a ring cannot be opened to absorb the -CHO carbon, so the suffix -carbaldehyde is used to name a -CHO carbon that lies outside the parent ring

   The suffix -al requires the -CHO carbon to be part of the numbered parent chain. When -CHO hangs off a ring, its carbon is not a ring atom, so the suffix -carbaldehyde is used instead.

   In substitutive nomenclature the suffix -al (and -oic acid, -nitrile) includes the functional carbon in the parent. Propanal is a three-carbon chain in which C1 is the carbonyl carbon. A ring, however, is numbered as a closed unit and cannot absorb an extra carbon, so a -CHO attached to a ring atom has a carbon outside the parent. IUPAC covers exactly this case with the suffixes -carbaldehyde, -carboxylic acid and -carbonitrile, which explicitly denote a functional carbon additional to the parent hydride. Hence cyclohexanecarbaldehyde is C6H11-CHO (seven carbons in total, six in the ring). The same logic makes benzoic acid an exception based on a retained name, while cyclohexanecarboxylic acid follows the systematic pattern.

   Common mistake: Naming a ring aldehyde as 'cyclohexanal' or expanding the ring into a longer chain

   Key point: Suffixes with 'carb' (-carbaldehyde, -carboxylic acid, -carbonitrile) signal a functional carbon that is NOT part of the parent ring or chain.

5. Question 5 · medium · IUPAC nomenclature

   What is the correct IUPAC name of C6H5-CH2-COOH, and which part of the molecule is chosen as the parent?

   • A.2-Phenylacetic acid (phenylethanoic acid): the two-carbon chain bearing -COOH is the parent, and the benzene ring is cited as the substituent prefix phenyl
   • B.Benzenecarboxylic acid, taking the ring as parent because a ring always outranks a chain in IUPAC nomenclature
   • C.Benzylmethanoic acid, treating the -COOH carbon as a one-carbon parent and the whole C6H5CH2- unit as a benzyl substituent
   • D.Toluene-1-carboxylic acid, treating the methyl-substituted ring as parent
   Show answer and explanation

   Answer: A. 2-Phenylacetic acid (phenylethanoic acid): the two-carbon chain bearing -COOH is the parent, and the benzene ring is cited as the substituent prefix phenyl

   The principal characteristic group -COOH sits on a chain carbon, so the chain containing it (two carbons) is the parent; the ring becomes the phenyl prefix, giving 2-phenylacetic acid (phenylethanoic acid).

   Parent selection is decided by the principal characteristic group, not by size or by ring-versus-chain status. Here -COOH is attached to a CH2 group, so the carbon chain containing the acid carbon is C(=O)OH-CH2-, a two-carbon chain named ethanoic (acetic) acid. Everything else, the C6H5 unit, becomes a substituent prefix, phenyl, located on C2. The accepted names are therefore 2-phenylacetic acid or phenylethanoic acid. Benzoic acid (option B) has -COOH bonded directly to a ring carbon and formula C7H6O2, whereas our compound is C8H8O2. Option C wrongly shortens the parent to one carbon, and option D misplaces the acid group on the ring.

   Common mistake: Assuming the benzene ring must always be the parent because it is the largest fragment

   Key point: The parent must contain the principal characteristic group; a benzene ring that does not carry it is only a phenyl prefix.

6. Question 6 · medium · IUPAC nomenclature

   What is the IUPAC name of CH2=CH-CH2-CH(OH)-CH3?

   • A.Pent-1-en-4-ol, numbering from the end nearer the double bond because unsaturation is always given the lower locant
   • B.4-Hydroxypent-1-ene, citing the -OH as a prefix because the chain already carries an -ene suffix
   • C.Pent-4-en-2-ol, because -OH is the principal characteristic group and must receive the lowest possible locant, which is 2
   • D.Pent-4-en-1-ol, obtained by giving the -OH carbon number 1 regardless of where it lies in the chain
   Show answer and explanation

   Answer: C. Pent-4-en-2-ol, because -OH is the principal characteristic group and must receive the lowest possible locant, which is 2

   The five-carbon chain carries -OH (principal group) and a C=C. Numbering from the CH3 end puts -OH at C2 and the double bond at C4, giving pent-4-en-2-ol.

   Both a double bond and a hydroxyl group are present. The hydroxyl group is the principal characteristic group and is expressed as the suffix -ol; the double bond is expressed by the infix -en-. The numbering hierarchy is: principal characteristic group first, then unsaturation, then substituent prefixes. Numbering from the CH3 end gives -OH at C2 and C=C between C4 and C5 (locant 4); numbering from the vinyl end gives -OH at C4 and C=C at 1. Since 2 < 4 for the -OH, the first direction wins and the name is pent-4-en-2-ol. Option A reverses the hierarchy, option B needlessly demotes -OH to a prefix, and option D ignores that the -OH is on an internal carbon.

   Common mistake: Giving the double bond the lower number because it is 'part of the skeleton'

   Key point: Principal characteristic group beats unsaturation for the lowest locant; unsaturation only decides when the group leaves a tie.

7. Question 7 · easy · IUPAC nomenclature

   In current IUPAC style the compound CH2=CH-CH=CH2 is written as buta-1,3-diene rather than 1,3-butadiene. What does this style change reflect?

   • A.That the compound contains two double bonds separated by exactly one single bond, which the older style could not indicate
   • B.That locants are placed immediately before the part of the name to which they refer, and the terminal 'a' of the stem is kept before a consonant-initial suffix such as -diene
   • C.That the parent is now considered to be butane rather than butene, so the stem changes from but- to buta-
   • D.That the two double bonds are chemically non-equivalent and the numbers 1 and 3 now denote their relative reactivities
   Show answer and explanation

   Answer: B. That locants are placed immediately before the part of the name to which they refer, and the terminal 'a' of the stem is kept before a consonant-initial suffix such as -diene

   Modern IUPAC places each locant directly before the affix it qualifies, and the stem keeps its terminal 'a' before a consonant, giving buta-1,3-diene.

   Two conventions are at work. First, locants are cited immediately in front of the suffix or infix they refer to, so '1,3' sits right before '-diene' instead of at the front of the whole name. Second, the elision rule: the terminal 'a' of the stem (buta-) is dropped only before a vowel-initial suffix (butan-1-ol, but-1-ene), and is retained before a consonant-initial suffix such as -diene, giving buta-1,3-diene. Both names describe the same molecule, and the change conveys nothing about conjugation, parent hydride identity or reactivity, which rules out options A, C and D.

   Common mistake: Assuming the spelling change signals a structural or electronic difference

   Key point: Locants sit next to the affix they describe; the stem 'a' is dropped only before a vowel-initial suffix.

8. Question 8 · easy · IUPAC nomenclature

   Which structure corresponds to the name propyl ethanoate?

   • A.CH3-CH2-CH2-CO-O-CH3, since the group named first in the name always supplies the acyl portion
   • B.CH3-CH2-CO-O-CH2-CH3, pairing a propanoyl unit with an ethyl group
   • C.CH3-CH2-CH2-O-CH2-CH3, an ether formed from propanol and ethanol
   • D.CH3-CO-O-CH2-CH2-CH3, an ethanoyl group joined through oxygen to a propyl group
   Show answer and explanation

   Answer: D. CH3-CO-O-CH2-CH2-CH3, an ethanoyl group joined through oxygen to a propyl group

   In 'alkyl alkanoate' the first word names the alkyl group attached to the ester oxygen and the second names the acid part, so propyl ethanoate is CH3-CO-O-C3H7.

   Esters are named as two separate words: the alkyl (or aryl) group bonded to the single-bonded oxygen comes first, and the acyl portion derived from the acid comes second with the suffix -oate. 'Ethanoate' comes from ethanoic acid, CH3COOH, so the acyl fragment is CH3-CO-. 'Propyl' is CH3CH2CH2- attached to the ester oxygen. Combining gives CH3-CO-O-CH2CH2CH3, molecular formula C5H10O2. Option A is methyl butanoate, option B is ethyl propanoate (both isomers of the correct answer), and option C is an ether, which has no carbonyl at all.

   Common mistake: Assigning the first-named group to the acyl side, which produces the isomeric ester

   Key point: In an ester name the first word is the group on oxygen; the -oate word carries the carbonyl carbon.

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