Help Naming Hydrocarbons | Explanation & Examples | Attached File

[fatcats]

Homework Statement

See attached file

Homework Equations

N/A

The Attempt at a Solution

a) 1,1,2-tribromo-1-propene

Now this one I'm not sure about. Is the CH3 a methyl group attached to ethene?
How can I consistently tell the main hydrocarbon chain in a diagram like this?

b) 1,2-butanediol

quite sure this one is right

c) 1-fluoro-4-methyl-3-pentanone

Second least sure about this one

 

[Borek]

How can I consistently tell the main hydrocarbon chain in a diagram like this?

Which is longer: propane or ethane? (bond multiplicity doesn't matter)

 

[fatcats]

what is bond multiplicity?
ethane is longer, but I can't tell if the CH3 is a methyl subgroup or if its part of the main chain because it's placed diagonally in the diagram

 

[Borek]

Doesn't matter if the bond is single, double or triple.

it's placed diagonally in the diagram

Doesn't matter, carbon chains are (almost) never exactly straight, even if they are drawn this way. Most often (when all carbons are saturated) the chain zigzags with angles being given by sp³ hybridization. Also remember single bonds are free to rotate.

 

[fatcats]

Okay, thank you for the information. I still don't understand what bond multiplicity is

a) 1,1,2-tribromo-1-propene
so this one is right then?
c) 1-fluoro-4-methyl-3-pentanone
is this one?

 

[fatcats]

If the bonds are free to rotate can't it just be a methyl group rotating as well as a carbon atom part of the main chain?

 

[Borek]

As far as I am aware technically correct names should look a bit different:

1,1,2-tribromoprop-1-ene
butane-1,2-diol
1-fluoro-4-methylpentan-3-one

If memory serves me well the way you named them (1-propene, 3-pentanone) was correct at some point in the past.

I still don't understand what bond multiplicity is

It is not a formal term, but I though it should be more or less obvious what I mean (perhaps my English failed me). When you have two carbon atoms they are bonded to each other with a single bond, double bond or a triple bond - these are bonds of different multiplicities, for selecting the longest chain kind of a bond between carbon atoms (its "multiplicity") doesn't matter.

If the bonds are free to rotate can't it just be a methyl group rotating

If you add a methyl group at the end of the carbon chain carbon chain got longer. If you add methyl group at the end of ethane you don't get methylethane, but propane.

Bond rotation means that it typically doesn't matter how the molecule is drawn, all the molecules below are just hexane.

 

[fatcats]

Thank you so much for your detailed response. It has clarified a lot for me.

I think my course expects me to name them the way I did; I was not aware it was an outdated method... this is for chem 12 in Ontario, Canada.

As for bond multiplicity your English is perfect. I have been seeing this term around but it was not explained in my course and when I tried to research it on the internet I did not really find any good clarification. I think I understand it now.

Alright so ethane and methane can't have methyl groups? I don't remember my course mentioning this but I will take your word for it.

The drawings as well were very helpful.

 

[Borek]

Alright so ethane and methane can't have methyl groups? I don't remember my course mentioning this but I will take your word for it.

It is not like they can't - just when you add a methyl group what you get is another compound that has its own name. When you add 1 to 4 you get 5, you won't refer to it as to "four with added one", won't you?

 

[fatcats]

But if butane gets a methyl group stemming from its 2nd or 3rd carbon, it's 2-methyl-butane?

If it's a side group attached to the end can't it be 1-methyl-butane or does it just become pentane?

 

[Borek]

If it is a side group, it is methyl, if it is attached at the end it is not a side group.