Organic Chemistry — Part 1: 40 MCQs with Explanations

Isopropyl alcohol ((CH₃)₂CHOH) has -OH group attached to a carbon bonded to two other carbon atoms.

Four-carbon chain with aldehyde group: butanal.

Pentane has three structural isomers: n-pentane, isopentane (2-methylbutane), and neopentane (2,2-dimethylpropane).

Starch is a natural polymer of glucose found in plants. Others are synthetic polymers.

tert-Butyl alcohol ((CH₃)₃COH) has -OH attached to carbon bonded to three other carbons.

Aldehydes reduce Tollens' reagent to give silver mirror. Acetaldehyde is an aldehyde.

Carboxylic acids contain carboxyl functional group (-COOH).

Polyethylene is polymerized from ethene (CH₂=CH₂) monomers.

Aldehydes contain formyl group (-CHO).

Low-density polyethylene (LDPE) and high-density polyethylene (HDPE) are commonly used for plastic bags.

Ketones contain carbonyl group (-CO-) bonded to two carbon atoms.

Teflon (polytetrafluoroethylene, PTFE) has non-stick properties and high heat resistance.

Alcohols contain hydroxyl functional group (-OH) attached to sp³ hybridized carbon.

Neoprene (polychloroprene) is a synthetic rubber used in wetsuits, gaskets, and hoses.

Cellulose is a polysaccharide polymer of glucose. Glucose is monosaccharide; sucrose and lactose are disaccharides.

(CH₃)₂CHOH (isopropanol) has the -OH group attached to a carbon bonded to two other carbon atoms, making it a secondary alcohol.

CH₃CH₂COOH has three carbon atoms with carboxylic acid functional group, so propanoic acid.

C₄H₁₀ has two structural isomers: n-butane (CH₃CH₂CH₂CH₃) and isobutane ((CH₃)₂CHCH₃).

Ethene (C₂H₄) undergoes electrophilic addition with bromine, decolorizing bromine water. Benzene requires catalyst for substitution. Cyclohexane and ethane are saturated and unreactive.

Glucose is a monosaccharide (monomer), not a polymer. Polyethylene, polyester, and nylon are synthetic polymers.

(CH₃)₃COH (tert-butanol) has the -OH group attached to a carbon bonded to three other carbon atoms, making it a tertiary alcohol.

Acetaldehyde (CH₃CHO) is an aldehyde that reduces Tollens' reagent ([Ag(NH₃)₂]⁺) to give silver mirror. Ketones, alcohols, and carboxylic acids do not give this test.

Hydrocarbons are organic compounds that consist exclusively of hydrogen and carbon atoms.

Aqueous KOH provides OH- ions, which are strong nucleophiles. They attack the alkyl halide, substituting the halogen to form an alcohol. This is a nucleophilic substitution reaction.

The iodoform test is positive for ethanol and for compounds containing a CH3CH(OH)- group or a CH3C=O group. Ethanol (CH3CH2OH) has the necessary CH3CH(OH)- structure to be oxidized to the methyl ketone.

Aldehydes and ketones undergo nucleophilic addition with HCN. The CN- ion attacks the carbonyl carbon, yielding a cyanohydrin. With acetaldehyde, it forms acetaldehyde cyanohydrin (CH3CH(OH)CN).

Nylon is a polyamide formed by a condensation reaction between a diamine and a dicarboxylic acid, with the elimination of a small molecule like water. The others are addition polymers.

Methane (alkane) reacts with chlorine in diffused sunlight via a free radical mechanism, where chlorine atoms substitute hydrogen atoms. This is a substitution reaction (halogenation).

Tollen's reagent ([Ag(NH3)2]+) is a mild oxidizing agent. Aldehydes are easily oxidized to carboxylic acids, reducing Ag+ to a silver mirror on the test tube. Ketones do not react.

The general formula for alkanes is CnH2n+2. For n=5, H = 2*5 + 2 = 12. This is pentane, C5H12.

The acidity of phenol is due to the resonance stabilization of the phenoxide ion (C6H5O-), which delocalizes the negative charge over the benzene ring. This stabilization is not possible in alkoxide ions (RO-).

Tollen's reagent tests for aldehydes. Acetone is a ketone and does not have an oxidizable aldehyde group, so it does not give a positive silver mirror test.

Natural rubber is a polymer of isoprene (2-methyl-1,3-butadiene).

Isomers have the same molecular formula but different structures. 2-Methylpropane (isobutane) has the formula C4H10, same as butane, but a branched structure. Cyclobutane is C4H8, Butene is C4H8, and Butyne is C4H6.

The aldehyde functional group is -CHO, consisting of a carbonyl group (C=O) bonded to at least one hydrogen atom.

Alkenes are commonly prepared by the dehydration of alcohols. This involves removing a water molecule from an alcohol in the presence of an acid catalyst like concentrated H2SO4.

Saponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of a carboxylic acid (soap). It is the reaction used to make soap from fats and oils.

Alkanes are saturated hydrocarbons with general formula CₙH₂ₙ₊₂. They are relatively unreactive and were historically called 'paraffins' (from Latin parum affinis, meaning 'little affinity').

Alcoholic KOH is a strong base and favors elimination reactions (dehydrohalogenation). It removes a hydrogen atom from a β-carbon and a halogen atom from the α-carbon, forming an alkene.

Macromolecules are very large molecules with high molecular weights. Proteins, DNA, and starch are polymers made of monomers. Glucose (C₆H₁₂O₆) is a simple monosaccharide monomer, not a macromolecule.