Correctness of writing H3C as opposed to CH3 in a carbon chain?

Question

I have been studying alkanes, alkenes & alkynes for a while, and I see in the examples that all the basic structural formulas start with $\\ce{CH3}$, then $\\ce{CH2}$, and the last carbon atom is $\\ce{CH3}$, but the one that is attached to the single/double/triple bond is $\\ce{CH}$. (Please correct me if I'm explaining it with the right terms.) Anyways, there's a question about drawing the structural formula for compounds. > Draw a structural formula for hex-3-ene. What my answer is: $$\\ce{CH3CH2CH=CHCH2CH3}$$ I thought this was right, then I looked at the solutions and it was $$\\ce{H3CCH2CH=CHCH2CH3}$$ So now my question is, why does it start with $\\ce{H3C}$ not $\\ce{CH3}$ like some other examples?

Answer 1

The methyl group is CH3- meaning it is C with 3 H atoms bonded to it and a free 4th bond to bind to the remaining portion of the molecule (represented simply as R', R'', or R''' so forth).

As your studies continue you will see the C of the methyl group becomes the dominant player of the methyl group bc this is where the bonding electrons to form the 4th bond are located. H can form only one bond.

So later on when you start doing reactions (rxns) the C is usually written first bc you move electrons to where they are moving to with the arrow and not the other way around. This is important: head of arrow goes in direction of electron movement; tail of arrow is at atom from which electrons came from (C in this case).

For your specific question re hex-3-ene you probably got dinged bc you placed the double bond in the wrong place in the molecule. It is between Cs 3 and 4 starting numbering so as to get to the lowest C. Go left to right or right to left. so C-C-C=C-C-C either from left or right is the 3rd carbon. Its easiest to eliminate the H so you can see the C backbone. Then fill in so 4 bonds around each C. CH3- is abbreviated Me for methyl so easier structural formula is Me-CH2-CH=CH-CH2-Me

Hope this helps. Nomenclature can be though since chem books are not uniform on the subject. Klein uses line notation which can really make it difficult to visualize a molecule. I recommend a ball and stick kit which can usually be purchased from a college bookstore for $10-20. Just make sure you get one for organic chem and not inorganic chem so you have the right "bonds" for your molecules. Good luck! Alison D.