Why four degree hydrogen is not possible?give explanation with possible answer .

Hydrogen is named 1deg , 2deg.... depending upon the carbon to which it is attached to. Hydrogen attached to a carbon which is linked only to another carbon for ex in ethane all hydrogens are 1deg, in propane the first and last carbons are 1deg and the middle carbon is a 2deg because it is linked to two carbons excluding it and so on.

 

                               In order to have a 4deg hydrogen it should be attached to a carbon which is linked to four other carbons excluding it but as we know the valency of carbon is 4 and it doesn’t even have any d-orbitals so it cannot accept a hydrogen and does not form a bond. Hence there is no possibility of having a 4^th deg hydrogen