1. Under SN2 conditions, on reaction with NaOH, (R)-2-bromo octane gives ____________
a) (S)-2-octanol
b) (R)-2-octanol
c) Trans-2-butene
d) Cis-2-butene
Explanation: Under SN2 conditions, on reaction with NaOH, (R)-2-bromo octane gives (S)-2- octanol. In SN2 mechanism, one bond is broken and one bond is formed synchronously.
2. Under SN2 conditions, on reaction with NaOH, (S)-2-bromo octane gives (R)-2-octanol. This is an example of ____________
a) Dynamicselective
b) Stereoselective
c) Regioselective
d) Stereospecific
Explanation: Under SN2 conditions, on reaction with NaOH, (S)-2-bromo octane gives (R)-2-octanol. This is an example of stereospecific reaction. In SN2 mechanism, one bond is broken and one bond is formed synchronously.
3. Optical purity is defined as the ____________
a) Ratio of rotation of pure enantiomer to rotation of mixture
b) Ratio of rotation of mixture to rotation of pure enantiomer
c) Product of rotation of mixture and rotation of pure enantiomer
d) Sum of rotation of mixture and rotation of pure enantiomer
Explanation: Optical purity is defined as the ratio of rotation of mixture to rotation of pure enantiomer. It is expressed as a percentage. If the sample only rotates plane-polarized light half as much as expected, the optical purity is 50%.
4. The formula of enantiomeric excess is ____________
a) [(d+l)/(d-l)]*100
b) [(d)/(d+l)]*100
c) [(d-l)/(d)]*100
d) [(d-l)/(d+l)]*100
Explanation: The formula of enantiomeric excess is [(d-l)/(d+l)]*100. It gives the percentage of excess of an enantiomer.
5. Conformations are different arrangements of atoms that can be converted into one another by rotation about ___________
a) Covalent bond
b) Double bond
c) Single bond
d) Triple bond
Explanation: Conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted exclusively by rotations about formally single bonds. Such isomers are generally referred to as conformational isomers or conformers and, specifically, as rotamers.
6. The energy required to rotate n-butane molecule about the carbon-carbon bond is called ___________
a) Rotational energy
b) Torsional energy
c) Enantiomeric energy
d) Potential energy
Explanation: The energy required to rotate n-butane molecule about the carbon-carbon bond is called torsional energy. Torsion energy can be used to solve problems of general relativity especially the singularity problem.
7. The rotation about the (C2 – C3) carbon-carbon bond of n-butane requires the energy of about ___________
a) 100 kJ/mol
b) 50 kJ/mol
c) 10 kJ/mol
d) 3 kJ/mol
Explanation: The rotation about the (C2 – C3) carbon-carbon bond of n-butane requires the very less energy of about 3kJ/mol. It requires very less amount of energy.
8. The infinity of intermediate conformations are called ___________
a) Skew conformations
b) Staggered conformations
c) Eclipsed conformations
d) Gauche
Explanation: The infinity of intermediate conformations are called skew conformations. Three conformations of cyclohexane, designated as chair, boat, and skew (or twist), are essentially free of angle strain.
9. The potential energy of n-butane is minimum for ___________
a) Skew conformations
b) Staggered conformations
c) Eclipsed conformations
d) Gauche
Explanation: The potential energy of n-butane is minimum for staggered conformations. It is because of no steric hindrance.
10. The potential energy of n-butane is maximum for ___________
a) Skew conformations
b) Staggered conformations
c) Eclipsed conformations
d) Gauche
Explanation: The potential energy of n-butane is maximum for eclipsed conformations. It is because of overlapping of functional groups.