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.
1 Aromatic Functional Group. 2  The aromatic hydrocarbons are a fourth class of organic compounds with only carbon and hydrogen. We recognize the alkanes, alkenes and the alkynes from their formulas which follow the general formula as shown below, Hydrocarbon.