Out here in the stroma, a bunch of different enzymes use the carbon dioxide molecules and hydrogen ions made during the light dependent phase to assemble sugar fragments which are half of a glucose molecule (just 3 carbon atoms, instead of the 6 required to make a complete glucose molecule).
An alkane, by definition, only has single bonds. Even if your second diagram made sense (it doesn't for the reason above) it would not be an alkane at all because there is a double bond. Alkanes are a functional group. It's called alkil. As a functional group they have the generic formula R(CH2)nH.
Functional groups: Atoms or groups of bonded atoms that bond to carbon atoms to give rise to other families of organic compounds. A given functional group will generally undergo the same type of reactions regardless of the molecule in which it appears.When a functional group is bonded to an atom, it is called a substituent of that atom.thers: Molecules containing two alkyl groups bonded to the same oxygen atom. Epoxides: Ethers containing an oxygen atom bonded to two other carbon atoms in a three-membered ring. Carbonyls: Molecules containing one or more carbonyl groups.