Organic Chemistry> Why para dihydroxy benzene does not have ...

Why para dihydroxy benzene does not have zero dipole moment while para xylene has. Both r electron donating towards benzene ring.

Dattatray Biradar , 9 Years ago

Grade 12th pass

3 Answers

Umakant biswal

Last Activity: 9 Years ago

@ dattatray
the dipole moment of para dimethoxybenzene is not 0 beacuse it exist in two forms , cis and trans forms .
out of which trans have 0 dipole moment beacuse it is a symmetrical molecule , whereas in the case of cis molecule , it is not completely symmetrical , therefore it have the dipole moment of 2.25 D .
as in solution , both forms coexist , therefore the observed dipole moment is more than 0 , but less that 2.25 D .
u can try out this by the structure also .
HOPE IT CLEARS YOUR DOUBT
ALL THE BEST , IN CASE OF ANY DOUBT , LET ME KNOW ..

Dattatray Biradar

Last Activity: 9 Years ago

dear umakant Sir thanks for inputs. However not much clear and my question still remains same - as per book paradimethyl benzene (p-xylene) has zero dipole moment while, paradihydroxy benzene has more than zero. Book says paradihydroxy benzene is non linear and thus dipole moment is not equal to zero. Is there Anything to do with lone pair on oxygen?

Sayan Bhowmik

Last Activity: 8 Years ago

Well It is simple. There are two possible planar configurations of para hydroxyphenol, one having zero dipole moment and the other have very small dipole moment (~1.4 D).Dipole moment is present because there is restricted rotation with the hydroxyl groups.. Dipole moment of O is cancel out but the dipole moment of H is added up as a vector sum bcz the 2 H are not at 180°..I hope my answer clear your doubt.