Free Fundamental Principles of Organic Chemistry MCQs with Answers

• A. forms four covalent bonds and can catenate into long chains and rings
• B. readily forms ions of charge four
• C. has a very large atomic radius
• D. always forms only single bonds

Explanation: With four valence electrons and a small radius, carbon forms four strong covalent bonds and bonds to itself almost as strongly as to other…

• A. has the same molecular formula
• B. differs from the next by a CH2 group and shares the same general formula and functional group
• C. has the same physical properties
• D. contains the same number of carbon atoms

Explanation: Members share a general formula and a functional group, so their chemical properties are similar, while physical properties such as…

• A. Benzene
• B. Cyclohexane
• C. Pyridine
• D. Naphthalene

Explanation: A heterocyclic compound has a ring containing at least one atom other than carbon, and in pyridine one of the six ring positions is…

• A. a hydroxyl group
• B. a carbonyl group at the end of the chain, written CHO
• C. a carboxyl group
• D. a carbonyl group between two carbon atoms

Explanation: In an aldehyde the carbonyl carbon carries at least one hydrogen and so must be terminal, whereas in a ketone the same carbonyl group lies…

• A. an alkane
• B. an alkyne
• C. an alcohol
• D. an alkene or a cycloalkane

Explanation: Both an alkene, with one double bond, and a cycloalkane, with one ring, have two hydrogens fewer than the corresponding alkane, so they…

• A. COOH
• B. CHO
• C. OH
• D. CO

Explanation: The carboxyl group combines a carbonyl and a hydroxyl on the same carbon atom, and this arrangement makes the hydrogen far more acidic…

• A. isotopes
• B. isomers
• C. homologues
• D. allotropes

Explanation: Isomers share the molecular formula but differ in how the atoms are connected or arranged in space, so they are genuinely different…

• A. chain isomers
• B. functional group isomers
• C. position isomers
• D. geometric isomers

Explanation: The carbon skeleton and the functional group are the same in both, and only the position of the hydroxyl group along the chain differs…

• A. position isomers
• B. chain isomers
• C. optical isomers
• D. functional group isomers

Explanation: Ethanol contains a hydroxyl group while dimethyl ether contains an oxygen bridging two carbons, so the functional group itself differs and…

• A. the double bond prevents free rotation, fixing the groups on either side
• B. the molecule contains a chiral carbon
• C. the double bond rotates freely
• D. alkenes contain a ring

Explanation: The pi bond locks the two carbons in a fixed relative orientation, so substituents are held either on the same side, cis, or on opposite…

• A. two identical groups and two different ones
• B. four different atoms or groups
• C. at least one double bond
• D. three hydrogen atoms

Explanation: A carbon with four different substituents has no plane of symmetry, so its mirror image cannot be superimposed on it and the two forms are…

• A. one
• B. two
• C. three
• D. four

Explanation: Butane has an unbranched chain of four carbons and 2-methylpropane has a three carbon chain with a methyl branch, and no other arrangement…

• A. the number of methyl groups present
• B. the total number of carbon atoms
• C. the position on the main chain where the methyl group is attached
• D. the number of double bonds

Explanation: The parent chain is numbered from the end that gives substituents the lowest possible locants, so the methyl group here sits on the second…

• A. Ethene
• B. Ethyne
• C. Benzene
• D. Ethane

Explanation: A saturated hydrocarbon contains only single carbon to carbon bonds and therefore holds the maximum possible number of hydrogen atoms…

• A. donates a pair of electrons
• B. accepts a pair of electrons and is attracted to electron rich centres
• C. always carries a negative charge
• D. contains an unpaired electron

Explanation: Electrophile means electron loving, so such a species is electron deficient and attacks regions of high electron density such as a double…

• A. two free radicals
• B. two neutral atoms
• C. a positive and a negative ion, because both electrons go to one atom
• D. no change in the molecule

Explanation: In heterolytic fission the shared pair leaves with the more electronegative atom, giving oppositely charged ions such as a carbocation and…

• A. COOR, formed by replacing the acidic hydrogen of a carboxylic acid
• B. OH attached to a benzene ring
• C. NH2 attached to a carbon chain
• D. a carbon to carbon triple bond

Explanation: An ester is formed when a carboxylic acid reacts with an alcohol, water being eliminated, and the resulting group is responsible for the…

• A. Propan-1-ol and propan-2-ol
• B. Butane and 2-methylpropane
• C. Propanal and propanone
• D. Ethane and propane

Explanation: Propanal is an aldehyde and propanone a ketone, yet both have the molecular formula C3H6O, so they differ in functional group.

• A. a region of high electron density such as a double bond
• B. another nucleophile
• C. an electron deficient carbon atom, donating a lone pair to it
• D. only free radicals

Explanation: Nucleophile means nucleus loving, so these electron rich species, such as hydroxide, cyanide and ammonia, seek out carbon atoms made…

• A. CH3CH2OH
• B. CH3CHClCH2CH3
• C. CH3CH2CH3
• D. CH2Cl2

Explanation: In CH3CHClCH2CH3 the second carbon carries a methyl group, a chlorine, a hydrogen and an ethyl group, four different substituents, so it…