RE: Organic Chemistry

Hello all,

I am currently doing my AS chemistry and am struggling with the Organic section of it!

What I don't understand is what the brackets mean and also, a few specific structural formulae that I don't understand the displayed formula's of:

(C2H5)2CHCH(CH3)CH(CH3)2
Also, I have been given the structural formula but it looks more like a displayed formula as it has the double bonds and single bonds.
CH3-CH2-CH=CH2 what would the displayed formula for that be?

Also, I don't understand how to draw the skeletal formula as well?

Sorry, I know there are a lot of problems- but, I'll be giving reps for helping out!

Thanks!

The brackets mean two things. In a formula, they can be used to determine how many of a polyatomic is there.
For instance, if you write Magnesium Hydroxide, you write Mg(OH)_2.
Not MgO₂H₂ because the {OH^-} is the structure that bonds to Magnesium.

The brackets also help to indicate what is bonded to what.
For instance, CH₃CH₂CH₃ is just propane.
But say I stick a methyl group on the second carbon, i.e. methylpropane
I have to write it as CH₃CH(CH₃)CH₃ and the brackets show that the methyl group is branching off that second carbon (if you're reading left to right).

If I instead wrote it as CH₃CHCH₃CH₃ then it might be confusing as it appears to be butane. Of course, upon closer inspection we can see that it's wrong seeing as one carbon is making 3 bonds and another is making 5 bonds.

In this case: (C2H5)2CHCH(CH3)CH(CH3)2

The first carbon has two ethyl groups branching off it (and a hydrogen of course). The next carbon has a methyl group branching off it. The third carbon has two methyl groups branching off the end.
It helps to draw it out to visualise it, but the resulting molecule would be called:
4-ethyl-2,3-dimethylhexane (I hope)

NB: We draw double bonds in the structural formula to avoid any ambiguity.
Displayed structural formula by the way is drawing absolutely every single bond in the molecule.

Skeletal formula is like drawing the displayed formula, except you do not draw the hydrogen atoms and the number of carbon atoms is equal to the number of vertices.

For instance, take propane again.

It's not drawn as a straight line, otherwise how else could I know how long the molecule is. Instead, from one carbon to the next is a straight line. But then to the carbon after that, you draw a line at an angle. Think of the lines as bonds and place a carbon atom at the end of each line segment. Notice that no hydrogen atoms are shown. If I wanted to draw methylpropane, I would simply draw a line upwards at the second carbon (i.e. the pointy bit)