Structural isomerism.

[balloonsandhighlighters]

hi everyone,

This is a thread made for structural isomerism, as a lot of people don't quite undesrstand its concept. First off, we will start with explaining it and its concept, and after that, people can post problems to do with it.

Ok, so i'll tell you my doubts about it, as they're general and apply to many people's queries! First off, how do we draw an isomer as apparently there are different ways to do so (i think 2?) and also, how do we name them, because the steps for naming the isomer is different for each homologous series. For instance, methylpropane is the isomer for butANE, whereas but-1-ene is an isomer for butENE.


Everyone is welcome to explain its concept/ask questions/answer questions.

This is of course in preparation for the soon to come paper 3 chemistry!

Balloons. And highlighters. Yar.

 

[ThatReallyReallyWeirdDude]

Hmm
Well
It's sort of difficult to just explain the entire thing. The best thing would be for people to ask example questions.
I'd answer
Or ask for explanation in a specific area e.g. how to name the isomers.

 

[balloonsandhighlighters]

P

Hmm
Well
It's sort of difficult to just explain the entire thing. The best thing would be for people to ask example questions.
I'd answer
Or ask for explanation in a specific area e.g. how to name the isomers.

oK, you're right, it is hard to write all of them as you must be studying too, so how about this: you write a little bit, anything that comes to mind about structural isomerism, and then others can add in things that you didn't mention, and then others can add things that that person didn't mention, so then by the end, we have completed notes on structural isomerism!
If you can't, then thats ok, but to those who are reading this, please do, just type in a few things, and then others type in a few more things etc etc. So we'll have like a cycle of information regarding structural isomerism!

 

[ThatReallyReallyWeirdDude]

Alright then we can start with how the numbers work
Numbers are used to show where a branch, element or double bond is in a compound.
For example, butene - C4H8. However, butene could have it's double bond in two different places:
CH3-CH=CH-CH3 or CH2=CH-CH2-CH3
The first one has the double bond between the second and third carbon atom i.e. attached to the second carbon atom
So it is but-2-ene. The second* one is but-1-ene (edit: corrected mistake)
A more complicated example:

CH3-CH2-CHCl-CHCl-CH3 and CH2Cl-CH2-CHCl-CH2-CH3
They're both dichloropentane
The first however is 2-3-dichloropentane and the second is 1-2-dichloropentane
Note:
CH3-CH2-CHCl-CHCl-CH3 This looks like it's actually 3-4-Dichloropentane but you always start from the side which has the closest chlorine (or double bond, branch etc.)
That is the same as
CH3-CHCl-CHCl-CH2-CH3, but just looking from the other side.
If it was CH3-CHCl-CH2-CHCl-CH3, you can start from either side because they both have the first chlorine on the second carbon no matter which side you look at
The above is 2-4-Dichloropentane

Last of all, is the -yls. That is, methyl (CH3), ethyl (C2H7), pentyl (C3H9)...
I'll make diagrams and further explain this branching thing later.

 

[balloonsandhighlighters]

Alright then we can start with how the numbers work
Numbers are used to show where a branch, element or double bond is in a compound.
For example, butene - C4H8. However, butene could have it's double bond in two different places:
CH3-CH=CH-CH3 or CH2=CH-CH2-CH3
The first one has the double bond between the second and third carbon atom i.e. attached to the second carbon atom
So it is but-2-ene. The second* one is but-1-ene (edit: corrected mistake)
A more complicated example:

CH3-CH2-CHCl-CHCl-CH3 and CH2Cl-CH2-CHCl-CH2-CH3
They're both dichloropentane
The first however is 2-3-dichloropentane and the second is 1-2-dichloropentane
Note:
CH3-CH2-CHCl-CHCl-CH3 This looks like it's actually 3-4-Dichloropentane but you always start from the side which has the closest chlorine (or double bond, branch etc.)
That is the same as
CH3-CHCl-CHCl-CH2-CH3, but just looking from the other side.
If it was CH3-CHCl-CH2-CHCl-CH3, you can start from either side because they both have the first chlorine on the second carbon no matter which side you look at
The above is 2-4-Dichloropentane

Last of all, is the -yls. That is, methyl (CH3), ethyl (C2H7), pentyl (C3H9)...
I'll make diagrams and further explain this branching thing later.

Hi ok it seems like no one is contributing ahaha :/ But thanks for your help, may i ask, where do you get your info from? As in, how do you know this stuff?

 

[ThatReallyReallyWeirdDude]

Err
That's all my knowledge
Don't worry, after phys P6 hopefully people will come along
Ask me any questions you wish

 

[balloonsandhighlighters]

no i mean like what text book do you use to know all of this? Because my text book doesn't go into all that detail I know this might be too much to ask (and if so you don't have to do it) but would it be possible if you scanned you're source (text book/notes) on structural isomerism? Or is that too much to ask ? ? Its ok if you can't but i really don't know what to do and honestly i don't quite understand everything you wrote ( i understood about half of it ) Thanks for your time even if you can't scan / don't have a scanner etc.

 

[ThatReallyReallyWeirdDude]

no i mean like what text book do you use to know all of this? Because my text book doesn't go into all that detail I know this might be too much to ask (and if so you don't have to do it) but would it be possible if you scanned you're source (text book/notes) on structural isomerism? Or is that too much to ask ? ? Its ok if you can't but i really don't know what to do and honestly i don't quite understand everything you wrote ( i understood about half of it ) Thanks for your time even if you can't scan / don't have a scanner etc.

I'm reaaalllyyy sorry but that's not from my textbook.
Let me see what the syllabus says about isomerism, cause I don't want to be including extra information.

From syllabus:
Describe and identify structural
isomerism

So you wont have to be able to explain it like I did, as long as you can say look at a compound and give it's name or think of structural isomers.
ONe tip is that if they ask for structural isomer of carboxylic acids you can use an ester

 

[balloonsandhighlighters]

I'm reaaalllyyy sorry but that's not from my textbook.
Let me see what the syllabus says about isomerism, cause I don't want to be including extra information.

So you wont have to be able to explain it like I did, as long as you can say look at a compound and give it's name or think of structural isomers.
ONe tip is that if they ask for structural isomer of carboxylic acids you can use an ester

so if its not from a text book, then where from? Thanks again

 

[ThatReallyReallyWeirdDude]

so if its not from a text book, then where from? Thanks again

A mixture of googling, my head and my teacher. I also used to have this other book but it's lost now.