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.
Ch18 Ketones and Aldehydes (landscape) Page 5 A ketone or aldehyde group can also be named as a substituent on a molecule with another functional group as its root. The ketone carbonyl is given the prefix oxo -, and the aldehyde group is named as a formyl-group.(This is especially common for carboxylic acids).h18 Ketones and Aldehydes (landscape) Page 13 However, to circumvent this problem, carboxylic acids can be converted first into a functional group that is easier to reduce than an aldehyde group. The group of choice is an acid chloride.