The most common and most likely answer to this crossword clue is the 5 letter word ALKYL
A
L
K
Y
L
Buddy explains!
The straight part
We know that "alkane without a hydrogen atom" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case alkane without a hydrogen atom = alkyl.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ALKYL mean?
ALKYL noun- Any of a series of univalent radicals of the general formula CnH2n+1 derived from aliphatic hydrocarbons.