Question 1: Arrange the following compounds in order of decreasing acidity: (IIT- JEE 2013)
(a) I > II > III > IV
(b) III > I > II > IV
(c) IV > III > I > II
(d) II > IV > I >III
Solution: Electron donating groups increase the acidity of phenol when present as substituent on the benzene ring while electron withdrawing groups decrease the acidity of phenol.
Cl and NO2 are electron withdrawing groups while -CH3 and -OCH3 are electron donating groups.
However, nitro undergoes resonance also which allows it to better stabilize the negative charge of the oxygen as compare to chlorine and thus acidic character of nitrophenol would be higher than that of chloro phenol.
So, Nitrophenol is the most acidic compound here followed by chloro phenol.
Hence, the correct option is b.
Question 2: Which of the given statement(s) about N, O, P and Q with respect to M is (are) correct? (IIT-JEE 2012)
(a) M and N are non–mirror image stereoisomers.
(b) M and O are identical.
(c) M and P are enantiomers.
(d) M and Q are identical.
Solution: Fischer Projections of the molecules:
It is clear that:
M and N are non–mirror image stereoisomers.
M and O are the same molecules i.e. Identical.
M and P are the non-superimposable mirror images of hence they are enantiomers.
N and Q are identical.
M and Q are also are non–mirror image stereoisomers i.e diasteriomers.
Hence A, B and C are the correct statements.
Question 3: The total number of cyclic isomers possible for a hydrocarbon with the molecular formula C4H6 is (IIT-JEE 2010)
Solution: 5 cyclic isomers are possible for C4H6, possible.