Optical activity and specific rotation

27 questions on Optical activity and specific rotation from the Stereoisomerism chapter: 5 NEET level, 11 JEE Main, 11 JEE Advanced. Each one opens with its answer and solution.

• A solution of an optically active compound has specific rotation +24.0 (units: degree dm^-1 (g/mL)^-1). It is placed in a polarimeter tube 2.0 dm long at concen... NEET level
• A 50:50 mixture of the (R) and (S) enantiomers of a chiral compound shows no net optical rotation. The reason is that NEET level
• Which one of the following compounds is optically active (as a single enantiomer it would rotate plane-polarised light)? NEET level
• meso-Tartaric acid, (2R,3S)-2,3-dihydroxybutanedioic acid, is optically inactive although it has two stereocentres. This is because NEET level
• The (R) enantiomer of a compound has a specific rotation of +30.0 under certain conditions. Under identical conditions the specific rotation of the (S) enantiom... NEET level
• A mixture of the two enantiomers of a compound is prepared. The pure (+) enantiomer has [alpha] = +66.0 in the solvent used. The mixture shows [alpha] = +39.6 u... JEE Main level
• A sample contains 7.0 g of the (+) enantiomer and 3.0 g of the (-) enantiomer of a compound whose pure (+) form has [alpha] = +52.0 (same conditions). The speci... JEE Main level
• Optically pure (R)-X racemises in solution. The enantiomeric excess falls by a first-order process with rate constant 0.0462 h^-1. The time needed for the ee to... JEE Main level
• Which one of the following compounds is optically active? JEE Main level
• None of the following has an sp3 carbon bonded to four different groups. Which of them are chiral (optically active as single enantiomers)? JEE Main level
• Assertion (A): A racemic mixture of two enantiomers cannot be separated into its components by fractional distillation. Reason (R): Enantiomers have identical b... JEE Main level
• A racemic carboxylic acid (pm)-RCOOH is treated with enantiomerically pure (R)-1-phenylethylamine to form salts. Select the correct statements. JEE Main level
• (R)-X has [alpha] = -48.0 and (S)-X has [alpha] = +48.0 (units degree dm^-1 (g/mL)^-1). A solution contains 0.12 g/mL of (R)-X and 0.04 g/mL of (S)-X and is exa... JEE Main level
• A sample is 85% (R) and 15% (S). Pure (R) has [alpha] = -42.0. The expected specific rotation of the sample is JEE Main level
• A 3.0 g sample of a compound that is 80% (R) and 20% (S) is mixed with 2.0 g of its racemate. The enantiomeric excess of the combined 5.0 g sample is JEE Main level
• Which of the following mixtures is optically inactive overall? (Tartaric acid = 2,3-dihydroxybutanedioic acid; RR and SS are the chiral forms.) JEE Main level
• A 250 mL solution contains a partly resolved sample of compound Y at 0.0500 g/mL. In a 2.00 dm tube the observed rotation is -3.60 deg. Pure (-)-Y has [alpha] =... JEE Advanced level
• Optically pure (R)-Z racemises by a first-order process in solution (the observed rotation alpha is proportional to the ee). The observed rotation falls from +9... JEE Advanced level
• Consider the compound octa-2,6-diene-4,5-diol, CH3-CH=CH-CH(OH)-CH(OH)-CH=CH-CH3. Counting all configurational stereoisomers (E/Z isomers of both C=C bonds and ... JEE Advanced level
• Trihydroxyglutaric acid is HOOC-CH(OH)-CH(OH)-CH(OH)-COOH (2,3,4-trihydroxypentanedioic acid). Counting configurational stereoisomers, select the correct statem... JEE Advanced level
• How many of the following five compounds are chiral (optically active as single enantiomers)? (i) penta-2,3-diene; (ii) 3-methylbuta-1,2-diene; (iii) spiro[3.3]... JEE Advanced level
• Sample A (6.0 g) has [alpha] = +30.0 and sample B (4.0 g) has [alpha] = -10.0, both samples of the same compound whose pure (+) enantiomer has [alpha] = +50.0 u... JEE Advanced level
• A sample of (S)-enriched 2-butanol has ee = 40%. Pure (S)-2-butanol has [alpha] = +13.5 under the stated conditions. Select the correct statements. JEE Advanced level
• Assertion (A): (2R,3S)-2,3-dibromobutane is optically inactive, whereas (2R,3S)-2,3-dibromopentane is optically active. Reason (R): In 2,3-dibromobutane the two... JEE Advanced level
• Match the species in List I with the property in List II. List I: P = meso-tartaric acid; Q = (2R,3R)-tartaric acid; R = one enantiomer of penta-2,3-diene; S = ... JEE Advanced level
• Each of the following optically active ketones/aldehydes is kept in aqueous NaOH at room temperature. Select those that lose their optical activity by racemisat... JEE Advanced level
• 2,5-Dibromohex-3-ene, CH3-CHBr-CH=CH-CHBr-CH3, has two stereocentres and a C=C bond. Counting all configurational isomers, the number of them that are optically... JEE Advanced level