What is effect of donating group or withdrawing groups on hydrophobic characters on organic compounds. Is there any effect of addition of Methyl group (replacing H atom) on hydrophobic characters
Methyl group will increase the hydrophobicity. Usually organic aromatic and aliphatic compounds are insoluble in water and increase hydrophobicity. Functional groups (electron donating or withdrawing) that can form hydrogen bond with water can affect the hydrophobic behavior (like dissolve like).
Addition of alkyl group will again increase hydrophobicity, because of this you solubility difference will be there.
Addition of methyl group by removing H, it again increase hydrophobicity, so solubility in acidic solvents remains constant but in aqueous solvents decreases.
addition of methyl group will increase stability of your compound. the sensitive reactivity will be decreases.
Best to look up the Partition Coefficient of any substituent group that you are interested in. This allows one to calculate whether the addition of such a group to a molecule will increase or decrease the lipophilicity of the substance. Many books on drug design contain tables of these numbers. One such book, although old by now, is "Selective Toxicity" by Adrien Albert.
the effects of substituents (group) on hydrophobic characters of organic compounds which are decreased. This is because of hydrogen bonding and dipolar interaction hydrophilic characters are increased.