There are no way of makinf a structure having more than 2 carbons without any secondary carbon. Tertiary ok. But, secondary no way. When tou have two carbons, both are primary ones. Over this, atleast one of the m is secondary see: H2C -- CH2 -- CH3. The carbon is CH2 is a secondary one. H3C -- CH2 -- CH2 -- CH3. Both carbons in CH2 are secondary ones. I can only evision something like : 6CH4, 3C2H6, 4C2H6, etc.