Naming and Drawing Organic Compounds

Because I'm pretty lazy, I just photocopied my Chemistry holiday homework for this one.

Sorry that it's on a slight angle.

Rightio, let's start with 1a. It's always a good place to start!

First things first- identifying which homologous series the structure belongs to. There's only single bonds here, so it's an alkane and will therefore end with an -ane ending.

Secondly, we work out what the longest carbon chain is. No, it's not 4, it's actually 6. There's three on the top row, and then the third one joins on to the three on the bottom row. (Due to the nature of single bonds, rotations and flips and whatnot don't change the order of bonding- sorry, couldn't think of a clearer term. Anyway, diagrams don't even accurately show where the atoms are in relation to each other.) Therefore, we know that there's a hex- in there somewhere. So far, we've got ourselves "hexane."

But what about that extra CH3 joined on to the third atom? Well, that's called a "alkyl group." Because there's only one C atom, it's "methyl-." (If there were two carbons, it'd be ethyl-. Three would make it propyl-, and so on.)

Now, we also have to assign the alkyl group a number so that we know where to find it on the chain! Counting in one direction, the alkyl group's on the 3rd carbon. Counting in the other direction, it's on the 4th carbon. Always work with the lower numbers. Since 3 is lower than 4, we'll stick with 3. Finally, since there's only one methyl group, we don't need to worry about adding di- or tri- before the "methyl." (You don't need to add mono- either- if there's no prefixes, it's implied that there's only one.) Therefore, the final name is 3-methylhexane. Yay!

We can write this all down as a series of steps:

1. Figure out which homologous series the structure belongs to. This will give the suffix.
2. Count the number of carbons in the longest carbon chain.
3. Figure out the names and locations of all attachments to the chain that aren't hydrogen atoms. (This includes alkyl groups and halogens like bromine and iodine.) If there's more than one of anything, indicate this with a prefix like di- or tri-. Also, when giving locations of groups, make sure to give all the attachments the lowest possible numbers. List all attachments in alphabetical order.

Let's try these steps with 1e.

Homologous series- Alkane, as all single bonds. Hence -ane ending.

No. of carbons- 10, so dec-.

Extra bits and pieces:

1 x Chlorine at 2

1 x Fluorine at 5

3 (tri-) x Methyl at 3, 3 and 9

1 x Propyl at 5

Final name: 2-chloro-5-fluoro-3,3,9-trimethyl-5-propyldecane

I won't give worked examples of the other ones because I have to wake up at 6am tomorrow and I'm not a morning person, but I will give some pointers.

NO2 goes by the prefix nitro- and NH2- goes by the prefix amino-. However, you don't really have to worry about these in 2AB Chemistry.

You also don't need to worry about cycloalkyl groups in 2AB (as seen in 3c). They work pretty much the same way as an alkyl group. The trick is knowing whether you're dealing with a cycloalkane with alkyl groups or an alkane with cycloalkyl groups.

You do need to worry about cycloalkanes with alkyl groups. Labelling these is exactly the same as labelling alkanes with alkyl groups. The only difference is that cycloalkanes obviously don't have ends. The numbering goes clockwise. Just try and make it so that each alkyl group or halogen has the lowest numbering possible. Halogens should get preference for the lowest numbers.

Now for drawing hydrocarbons. I'm going to pick a semi-hard example so that I'll cover pretty much everything and will only have to explain once. The example I'm going to pick is 2i: 2,2-dichloro-6-methyl-4-propylheptane.

Drawing hydrocarbons is easier, in my opinion. Here are my steps:

1. Draw all of the carbons required.

2. Draw bonds between them according to the functional group.

3. Add all of the other bits and pieces on.

4. Draw on all of the hydrogen atoms. Yes, you have to do this step. My Chem teacher told us that this guy from another class offered his brother $5 if he would draw on all of the hydrogen atoms for him. The brother looked at how many he had to draw and said, "Not worth it!"

Obviously, you need to draw all of the bonds on but I kind of ran out of room and couldn't be bothered rearranging stuff.

So that's pretty much all of the basic stuff on naming and drawing organic compounds. I've only really covered alkanes, but alkenes and alkynes aren't too different. The only thing is that you need to put the location of the double and triple bond just before the -ene or -yne suffix (e.g. but-2-ene). If you want me to clarify, just ask!