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Conformational analysis of ethane, butane and cyclohexane

46 questions on Conformational analysis of ethane, butane and cyclohexane from the Stereoisomerism chapter: 8 NEET level, 19 JEE Main, 19 JEE Advanced. Each one opens with its answer and solution.

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Of the two extreme conformations of ethane, the more stable one is the NEET level
In the fully eclipsed conformation of butane (viewed along the C2-C3 bond) the dihedral angle between the two CH3 groups is NEET level
Among the conformations of butane obtained by rotation about the C2-C3 bond, the most stable one is NEET level
Of the following conformations of cyclohexane, the most stable is the NEET level
In a chair cyclohexane, an axial substituent on C1 experiences steric (1,3-diaxial) repulsion with the axial groups on NEET level
On ring flip of the chair conformer of methylcyclohexane that has the methyl group equatorial, the methyl group becomes NEET level
In the Newman projection of butane viewed along C2-C3, the front carbon has CH3 at 12 o'clock, H at 4 and H at 8 o'clock. The rear carbon, eclipsed with the fro... JEE Main level
Take butane as existing only as one anti conformer (energy 0) and two equivalent gauche conformers (each 3.8 kJ/mol above anti). Use R = 8.314 J K^-1 mol^-1 and... JEE Main level
Assume the axial conformer of a monosubstituted cyclohexane lies 7.0 kJ/mol above the equatorial conformer (the A-value). Using R = 8.314 J K^-1 mol^-1 and 298 ... JEE Main level
Which statement about the two geometric isomers of 1,3-dimethylcyclohexane is correct? JEE Main level
Select the correct statements about trans-1,4-dimethylcyclohexane. JEE Main level
The energies of some cyclohexane conformations relative to the chair (0) are: twist-boat 23, boat 30, half-chair 45 kJ/mol. The energy barrier for the chair-to-... JEE Main level
Match the butane conformations (dihedral angle between the two methyl groups, viewed along C2-C3) in List I with their descriptions in List II. List I: P = 0 de... JEE Main level
Assertion (A): The boat conformation of cyclohexane is less stable than the chair. Reason (R): In the boat conformation the C-C-C bond angles are about 90 deg, ... JEE Main level
In cis-1-tert-butyl-4-methylcyclohexane the A-values are tert-butyl 20.0 and methyl 7.3 kJ/mol (strain of the axial position relative to equatorial; assume addi... JEE Main level
In trans-1,2-dimethylcyclohexane the diequatorial chair has one gauche CH3/CH3 interaction, while the diaxial chair has four CH3/H 1,3-diaxial interactions. Tak... JEE Main level
In cis-1,3-dimethylcyclohexane, the diaxial chair has one CH3/CH3 1,3-diaxial interaction (15.4 kJ/mol) and two CH3/H 1,3-diaxial interactions (3.8 kJ/mol each)... JEE Main level
Count all configurational stereoisomers of 1,2,3-trimethylcyclohexane (enantiomers are counted separately and a meso form is counted once; conformers are not co... JEE Advanced level
2-Bromo-3-chlorobutane is drawn as a Newman projection viewed along C2 (front) to C3 (rear). Front carbon C2: CH3 at 12 o'clock, Br at 4 o'clock, H at 8 o'clock... JEE Advanced level
A Newman projection of 2,3-dibromobutane, viewed along C2 (front) to C3 (rear), shows: front carbon C2 with CH3 at 12 o'clock, Br at 4 o'clock, H at 8 o'clock; ... JEE Advanced level
Treat butane as having one anti conformer (energy 0) and two equivalent gauche conformers (each 3.8 kJ/mol above anti), ignoring all other conformers. Use R = 8... JEE Advanced level
Use for cis-1,2-dimethylcyclohexane: CH3/H 1,3-diaxial interaction = 3.8 kJ/mol and gauche CH3/CH3 interaction = 3.8 kJ/mol. Select the correct statements. JEE Advanced level
A-values (kJ/mol): tert-butyl 20.0, methyl 7.3, chlorine 2.2. Assume additivity of A-values and ignore other interactions. Select the correct statements. JEE Advanced level
Relative to the chair (0), the twist-boat of cyclohexane is 23.0 kJ/mol and the boat 30.0 kJ/mol higher. Use Boltzmann statistics at 298 K with R = 8.314 J K^-1... JEE Advanced level
In the Newman projection along C2-C3 of butane, the anti conformer has front CH3 at 12 o'clock and rear CH3 at 6 o'clock. The rear carbon is rotated by 60 deg s... JEE Advanced level
In cis-1,4-di-tert-butylcyclohexane, a chair necessarily has one tert-butyl group axial; assume this chair lies 26.0 kJ/mol above the all-equatorial reference, ... JEE Advanced level
The dihedral angle between the two methyl groups of butane (viewed along C2-C3) is varied. Using H/H eclipsing 4.0, H/CH3 eclipsing 6.0 and CH3/CH3 eclipsing 11... JEE Advanced level
cis-1,3,5-Trimethylcyclohexane is treated with CH3/CH3 1,3-diaxial interaction = 15.4 kJ/mol and ignoring all other interactions (each axial methyl has no other... JEE Advanced level
The barrier to rotation about the C-C bond in ethane is about 12 kJ mol^-1. Which conformation is the energy minimum, and why is the other less stable? NEET level
In the more stable chair conformation of tert-butylcyclohexane, the tert-butyl group occupies: NEET level
Which pairing of relative configuration and occupied chair positions (a = axial, e = equatorial) is correct for a disubstituted cyclohexane? JEE Main level
Consider cis-1-tert-butyl-4-methylcyclohexane. Take the A-value of CH_3 as 7.3 kJ mol^-1 and that of tert-butyl as much larger. Which statement is correct? JEE Main level
In butane, take these eclipsing increments: H/H = 4.0, CH_3/H = 6.0, CH_3/CH_3 = 11 (all kJ/mol), and gauche CH_3/CH_3 = 3.8 kJ/mol. A Newman projection along C... JEE Main level
Match the CH_3-C2-C3-CH_3 dihedral angles of butane in Column I with the conformation type in Column II. Column I: (P) 0 deg; (Q) 60 deg; (R) 120 deg; (S) 180 d... JEE Main level
Assertion (A): The two chair conformers of cis-1,2-dimethylcyclohexane have equal energy. Reason (R): Both chair conformers have two axial methyl groups. JEE Main level
Which sequence correctly lists cyclohexane conformations in increasing energy? JEE Main level
Which statements about cis-1,3-dimethylcyclohexane are correct? JEE Main level
What are the Br-C1-C2-Br dihedral angles in (i) the diequatorial conformer of trans-1,2-dibromocyclohexane, (ii) the diaxial conformer of trans-1,2-dibromocyclo... JEE Main level
For trans-1,2-dimethylcyclohexane at 298 K take: each CH_3/H syn-diaxial interaction = 3.7 kJ mol^-1 and one gauche CH_3/CH_3 interaction = 3.8 kJ mol^-1 (use R... JEE Advanced level
For cis-1,3-dimethylcyclohexane take: a CH_3/H syn-diaxial interaction = 3.7 kJ mol^-1 and a CH_3/CH_3 syn-diaxial interaction = 15.4 kJ mol^-1. What is the ene... JEE Advanced level
Menthol is (1R,2S,5R)-2-isopropyl-5-methylcyclohexan-1-ol (OH on C1, isopropyl on C2, CH_3 on C5). Which of the following stereoisomers can adopt a chair in whi... JEE Advanced level
For menthol, (1R,2S,5R)-2-isopropyl-5-methylcyclohexan-1-ol, in its preferred chair conformation, which statements are correct? JEE Advanced level
Menthyl chloride (Cl, isopropyl and CH_3 all equatorial in its preferred chair, with the same relative configuration as menthol) and neomenthyl chloride (Cl axi... JEE Advanced level
Which statements about the E2 elimination (anti-periplanar H and Br) of cis- and trans-1-bromo-2-methylcyclohexane are correct? JEE Advanced level
Butane exists as three staggered minima: one anti and two equivalent gauche conformers, with the gauche conformers 3.8 kJ mol^-1 above anti (neglect eclipsed fo... JEE Advanced level
Which statements about decalin (bicyclo[4.4.0]decane) are correct? JEE Advanced level