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What is the typical energy barrier range (in kJ mol$^{-1}$) that hinders the completely free rotation around a C-C single bond in alkanes?
The NCERT text mentions: 'It is hindered by a small energy barrier of 1-20 kJ mol–1 due to weak repulsive interaction between the adjacent bonds.' (Chapter: Hydrocarbons, Page 305)
Which of the following is NOT an alternative term for conformations?
The context defines conformations as 'spatial arrangements of atoms which can be converted into one another by rotation around a C-C single bond are called conformations or conformers or rotamers.' Tautomers are a different type of isomerism involving proton transfer and rearrangement of electrons. (Chapter: Hydrocarbons, Page 305)
How is the front carbon atom represented in a Newman projection?
According to the NCERT description of Newman projections: 'The carbon atom nearer to the eye is represented by a point.' (Chapter: Hydrocarbons, Page 305)
In a Sawhorse projection, the central C-C bond is depicted as:
The NCERT states for Sawhorse projections: 'It is then projected on paper by drawing the central C–C bond as a somewhat longer straight line.' (Chapter: Hydrocarbons, Page 305)
Why is the staggered conformation of ethane generally more stable than its eclipsed conformation?
The summary states: 'Out of staggered and the eclipsed conformations of ethane, staggered conformation is more stable as hydrogen atoms are farthest apart.' This minimizes torsional strain or repulsive interactions between electron clouds of C-H bonds. (Chapter: Hydrocarbons, Page 326)
Which projection method shows the rear carbon atom as a circle?
The NCERT text on Newman projections states: 'The rear carbon atom (the carbon atom away from the eye) is represented by a circle...' (Chapter: Hydrocarbons, Page 305)
If you keep one carbon atom stationary and rotate the other carbon atom around the C-C axis in ethane, what phenomenon is observed regarding the spatial arrangements of hydrogen atoms?
The NCERT states: 'This rotation results into infinite number of spatial arrangements of hydrogen atoms attached to one carbon atom with respect to the hydrogen atoms attached to the other carbon atom. These are called conformational isomers (conformers). Thus there are infinite number of conformations of ethane.' (Chapter: Hydrocarbons, Page 305)
Which of the following methods is not suitable for the preparation of aromatic primary amines?
According to the NCERT text, 'Aromatic primary amines cannot be prepared by this method [Gabriel phthalimide synthesis] because aryl halides do not undergo nucleophilic substitution with the anion formed by phthalimide.' Ammonolysis of aryl halides, conceptually similar to Gabriel phthalimide synthesis in its reliance on nucleophilic substitution, also faces limitations due to the low reactivity of aryl halides towards nucleophilic substitution. Reduction of nitro compounds, reduction of amides, and Hoffmann bromamide degradation are all viable methods for preparing aromatic primary amines.
An amine is obtained from an amide through a degradation reaction. This reaction results in an amine containing one carbon atom less than the starting amide. Which named reaction describes this process?
The NCERT states, 'Hoffmann developed a method for preparation of primary amines by treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide. In this degradation reaction, migration of an alkyl or aryl group takes place from carbonyl carbon of the amide to the nitrogen atom. The amine so formed contains one carbon less than that present in the amide.' This perfectly describes the Hoffmann bromamide degradation reaction.
Which of the following statements regarding the stability of substituted ammonium cations in protic polar solvents is correct?
The NCERT text mentions, 'Alkylamines are found to be stronger bases than ammonia. In alkylamines, a combination of electron releasing, steric and H-bonding factors influence the stability of the substituted ammonium cations in protic polar solvents and thus affect the basic nature of amines.' It also specifically states, 'Aliphatic amines are stronger bases than ammonia due to +I effect of alkyl groups leading to high electron density on the nitrogen atom.'
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