Question

Q. Which of the following compound has maximum number of primary H-atoms?$$\begin{gathered} 1.C{H}_{4}2.C{H}_3-C{H}_2-C{H}_3 \\ 3.C(C{H}_3{)}_{4}4.H_5{C}_2-CH-C{H}_3 \\ | \\ C{H}_3 \end{gathered}$$

Answer 1

Dear Student,

Primary hydrogens are the hydrogen attached to the primary carbon i.e. carbon which is bonded with only one other carbon atom.
$$\begin{gathered} 1)\mathrm{This}\mathrm{is}\mathrm{a}\mathrm{special}\mathrm{case},\mathrm{as}\mathrm{here}\mathrm{carbon}\mathrm{is}\mathrm{attached}\mathrm{to}\mathrm{no}\mathrm{other}\mathrm{carbon}.\mathrm{This}\mathrm{is}\mathrm{not}\mathrm{called}\mathrm{primary}\mathrm{carbon}\mathrm{and}\mathrm{hence}\mathrm{here}\mathrm{no}\mathrm{primary}\mathrm{hydrogens}\mathrm{are}\mathrm{present}. \\ 2)\mathrm{Here}\mathrm{both}\mathrm{the}\mathrm{terminal}\mathrm{carbons}\mathrm{are}\mathrm{primary}. \\ \mathrm{So},\mathrm{number}\mathrm{of}\mathrm{primary}\mathrm{hydrogens}=3+3=6 \\ 3)\mathrm{Here}\mathrm{all}\mathrm{the}4-{\mathrm{CH}}_3\mathrm{groups}\mathrm{are}\mathrm{attached}\mathrm{to}\mathrm{only}\mathrm{one}\mathrm{C}\mathrm{and}\mathrm{so}\mathrm{are}\mathrm{primary}. \\ \mathrm{Therefore},\mathrm{number}\mathrm{of}\mathrm{primary}\mathrm{hydrogen}=4\times 3=12 \\ 4)\mathrm{The}\mathrm{structure}\mathrm{is}{\mathrm{CH}}_3{\mathrm{CH}}_2\left({\mathrm{CH}}_3\right){\mathrm{CHCH}}_3 \\ \mathrm{Here}\mathrm{all}\mathrm{the}-{\mathrm{CH}}_3\mathrm{groups}\mathrm{are}\mathrm{primary}.\mathrm{SO},\mathrm{number}\mathrm{of}\mathrm{primary}\mathrm{H}=3\times 3=9 \\ \mathrm{So},\left(3\right)\mathrm{has}\mathrm{maximum}\mathrm{number}\mathrm{of}\mathrm{primary}\mathrm{H}-\mathrm{atoms}. \end{gathered}$$