The well-known compounds, (+)- lactic acid and (-)- lactic acid, have the same molecular formula, C₃H₆O₃. The correct relationship between them is:

• constitutional isomerism

• geometrical isomerism

• identicalness

• optical isomerism

Which one of the following characteristics belong to an electrophile?

• It is any species having electron deficiency which reacts at an electron-rich C-centre

• It is any species having electron enrichment, that reacts at an electron-deficient C-centre

• It is cationic in nature

• It is anionic in nature

183.

Among the following structures the one which is not a resonating structure of others is

• I

• II

• III

• IV

Among the following carbocations:

Ph₂C⁺CH₂Me (I), PhCH₂CH₂CH⁺Ph (II), Ph₂CHCH⁺Me (III) and Ph₂C(Me)CH₂ (IV), the order of stability is:

• IV > II > I > III

• I > II > III > IV

• II > I > IV > III

• I > IV > III > II

Which one of the following will show optical isomerism?

• OH-CH₂-CO₂H

• CH₃-CH(OH)-CO₂H

• (CH₃)₂-CH-CO₂H

• (CH₃)₂-C(Cl)-CO₂H

Among the following statements about the molecules X and Y, the one(s) which correct is (are)

• X and Y are diastereomers

• X and Y are enantiomers

• X and Y are both aldohexoses

• X is a D-sugar and Y is an L-sugar

Explain why aniline is not as basic as ammonia.

The two structures written below represent

• pair of diastereomers

• pair of enantiomers

• same molecule

• both are optically inactive

Which of the following carbocations will be most stable ?

• ${\mathrm{Ph}}_3{\mathrm{C}}^{+}$

• ${\mathrm{CH}}_3-\stackrel{+}{\mathrm{C}}{\mathrm{H}}_2$

• $({\mathrm{CH}}_3{)}_2\stackrel{+}{\mathrm{C}}\mathrm{H}$

• ${\mathrm{CH}}_2=\mathrm{CH}-\stackrel{+}{\mathrm{C}}{\mathrm{H}}_2$

A compound is formed by substitution of two chlorine for two hydrogens in propane. The number of possible isomeric compounds is

• 4

• 3

• 2

• 5