Ncert Solutions Chemistry Class 11th

4.34. The combining atomic orbitals should have comparable energies like, 1s orbital of one atom can combine with 1s atomic orbital of another atom, 2s can combine with 2s.

The combining atomic orbitals must have proper orientations so that they are able to overlap to a considerable extent.

The extent of overlapping should be large.

The resonance structures have

(i) The same positions of nuclei, and

(ii) The same number ofunpaired electrons.

The resonance effect is defined as 'the polarity produced in the molecule by the interaction of two π -bonds or between a π -bond and lone pair of electrons present on an adjacent atom'. The effect is transmitted through the chain. There are two types of resonance or mesomeric effect designated as +R and-R effect.

The atoms or substituent groups, whichrepresent +R or –R electron displacementeffects are as follows:

+R effect: – halogen, –OH, –OR, –OCOR, –NH2, –NHR, –NR2, –NHCOR,

– R effect: – COOH, –CHO, >C=O, – CN, –NO2

The presence of alternate single and double bonds in an open chain or cyclic system is termed as a conjugated system. These systems often show abnormal behaviour. The examples are 1, 3- butadiene, aniline and nitrobenzene etc. In such systems, the π -electrons are delocalised and the system develops polarity.

Hyperconjugation is a general stabilising interaction. It involves delocalisation of σ electrons of C—H bond of an alkyl group directly attached to an atom of unsaturated system or to an atom with an unshared p orbital. The σ electrons of C—H bond of the alkyl group enter into partial conjugation with the attached unsaturated system or with the unshared p orbital. Greater the hyperconjugation, greater will be the stability of alkenes.

No, hyperconjugation is not a temporary effect. It is a permanent effect.

(i) By fractional crystallisation

(ii) Simple distillation

(iii Distillation under reduced pressure.