Help Naming Hydrocarbons | Explanation & Examples | Attached File

In summary, the hydrocarbons discussed in this conversation are ethane, propane, butane, and 1-fluoro-4-methyl-3-pentanone. Propane is the longest chain, butane is the second shortest, and 1-fluoro-4-methyl-3-pentanone is the least certain.
  • #1
fatcats
34
1

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
 

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  • #2
fatcats said:
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)
 
  • #3
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
 
  • #4
Doesn't matter if the bond is single, double or triple.

fatcats said:
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.
 
  • #5
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?
 
  • #6
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?
 
  • #7
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.

fatcats said:
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.

fatcats said:
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.

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  • #8
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.
 
  • #9
fatcats said:
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?
 
  • #10
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?
 
  • #11
If it is a side group, it is methyl, if it is attached at the end it is not a side group.
 

Related to Help Naming Hydrocarbons | Explanation & Examples | Attached File

What are hydrocarbons?

Hydrocarbons are molecules that are composed of only hydrogen and carbon atoms. They can be found naturally in crude oil and natural gas, and are also commonly used as fuels.

Why is it important to name hydrocarbons?

Naming hydrocarbons allows scientists to accurately identify and differentiate between different molecules. This is important for understanding their properties and potential uses.

What is the naming convention for hydrocarbons?

Hydrocarbons are named based on the number and arrangement of their carbon atoms. The main types of naming conventions are IUPAC (International Union of Pure and Applied Chemistry) and common names.

How do you name a hydrocarbon using the IUPAC convention?

The IUPAC convention uses prefixes and suffixes to indicate the number and type of carbon atoms in a molecule. For example, methane has one carbon atom and is named using the prefix "meth-" while ethane has two carbon atoms and is named using the prefix "eth-".

What are some common mistakes when naming hydrocarbons?

Some common mistakes when naming hydrocarbons include not counting the number of carbon atoms correctly, not using the correct prefixes and suffixes, and not placing commas correctly in long hydrocarbon names.

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