Question { Bombay Tablet, 7872 }

Explain about nucleophilic, electrophilic and free radical
substitutions?

Answer

In nucleophilic substitution, a weak nuclephile is replaced
by a stronger one. Similarly in electrophillic
substitution, a weaker electrophile is replaced by a
stronger one.
In free radical substituion, two different molecules are
split into their radicals, by energy etc, and then
electrophile of one combine with the nucleophile of the
other and vice versa.
e.g. CH4+Cl2-----> CH3. + H. + Cl. + Cl.
CH3.+Cl.-----> CH3Cl
H.+Cl.---------> HCl
In the first step, radicals are formed and in the second
radicals of one are replaced by the other

Question { 3389 }

What is the difference between DNA and RNA?

Answer

1. RNA is single stranded while DNA double stranded.
2. RNA has ribose while DNA has deoxyribose sugar.
3. RNA is present in cytoplasm while DNA is present in nucleus.
4. RNA is formed from DNA by transcription while DNA is formed from pre-existing DNA by replication.

Question { 30483 }

What is difference between Base and Nucleophile?

Answer

Base is a specie that donates an electron pair or extracts a proton from other molecule. A neucleophile is a specie that attack on positive or electron deficient site. Both base and neucleophile have excess of electrons. They may be negatively charged, neutral or partial negative portion of a polar molecule. The main difference between them is that a base extract H from other molecule and neucleophile attaches to the molecule itself. It should be moved that a strong neucleophile is a weak base and vice versa e.g. Chloride is a strong neucleophile due to its small size and electronegative nature but it is a weak base because it does not give electron pair easily (outermost electrons are tightly bound due to small size). Similarly, Iodide is a strong base but weak neucleophile due to large size.