OCR AS - Chemistry Unit F322 - Chains, energy and resource - REVISION!

Someone explain please:

E/Z isomerism as an example of
stereoisomerism, in terms of restricted
rotation about a double bond and the
requirement for two different groups to be
attached to each carbon atom of the C=C
group,

cis-trans isomerism as a special case of
E/Z isomerism in which two of the
substituent groups are the same.


BUT E/Z and cis/trans are the same?
thanks.

Someone explain please:

E/Z isomerism as an example of
stereoisomerism, in terms of restricted
rotation about a double bond and the
requirement for two different groups to be
attached to each carbon atom of the C=C
group,

cis-trans isomerism as a special case of
E/Z isomerism in which two of the
substituent groups are the same.

BUT E/Z and cis/trans are the same?
thanks.

Basically, Cis isomerism is the same as z isomerism. The non hydrogen groups attached to the C=C are on the same size.

Trans isomerism is E isomerism. The non hydrogen groups are on opposite sides of the C=C bond.

Not always!
OK, to get stereoisomers, you have to have:

1) a carbon-carbon double bond, as that restricts rotation and locks the groups in place
2) each carbon in the C=C bond must have two different groups on it.

To decide on whether it's E/Z, look at carbon 1 in the C=C bond, and decide which group has the highest priority (highest Mr). Now look at carbon 2 in the C=C bond and decide which group has the highest mass. If they are on the same side (Ze same side) it is Z, if they are on opposite sides it is E (enemies)

For cis/trans - you still need two different groups on each carbon of the C=C bond. But this time you look at carbon 1 and ask yourself - does it have a group that is also on carbon 2. If the answer is yes then you can name it by cis/trans. If these two groups are on the same side it is cis, if they are on opposite sides it is trans.

E/Z is used when there are three different groups around the double bond. When there are two different non-hydrogen groups then E/Z or cis/trans can be used. So cis=Z and trans=E when there are two different non-hydrogen groups.

Remember that you cannot have stereoisomerism if there is only one non-hydrogen group around the double bond as the cis and trans isomers will look the same (there wont be any).

For the exam you don't need to know the difference, the question will say: is this an E or a Z isomer OR the question will say: is this a cis or a trans isomer

Purely for interest, this is the difference:

FlClC = CHI and isomers of this would be E/Z isomers

HClC = CFlH and isomers of this would not just be E/z isomers but will also be cis-trans isomers because there are two hydrogen groups. So a cis isomer would be with the hydrogens horizontally across from each other, and the trans with them diaganally opposite from each other

Hope that made sense

EDIT: woops, looks like two people just answered this before me :P

In a kind of 'thread revival' (though it's only been 2 days!):

What's everyone's favourite and least favourite module out of the 4 from unit 2?

I think I probably prefer the first one - 'Basic concepts' - though the fuel and polymer waste stuff can get a bit bland. And, to be honest, even though module 4 (The resources and green crap) is so boring, there's nothing too complex, so I'd probably say I dislike mod 2 (Alcohols and halogeno's) the most, 'cos there's just so much.

What do you guys think?

I hate all the questions which relate to how chemists are trying to reduce the impact on the environment. So basically green chemistry and the entire resources module. Are there any horrible modules like that at A2?

What do we need to know about Ziegler Nata?

Can someone please give the advantages/disadvantages of the Hydration of Ethene to make ethanol and fermentation of sugars? According to the mark scheme. I thought i had it somewhere but can't find it. Thanks x

Hydration of Ethene

Advantages

100% atom economy
95% yield

Disadvantages

Requires high temp (300 deg.), which means lots of fuel burned and CO2 produced
Requires high pressures, which are expensive and dangerous
Ethene comes from Crude oil, which is non renewable

Fermentation of Glucose

Advantages

Comes from plants, which are renewable
Requires low temperatures (37 deg.) and pressures

Disadvantages

14% yield (as enzyme is denatured after this)
Low atom economy
Anaerobic conditions are necessary

How's it going guys?

ugh, I'm still struggling on the remembering of catalysts. I'm fine on processes/the maths side of things but I just can't memorise the catalysts. All I've got so far is: Hydrogenation of margarine: 150 degrees, nickel catalyst. Hydrolysis of ethene to make ethanol: phosphoric acid. Platinum/Rubidium/Palladium are used in a catalytic converter. Acidified dichromate is used to oxidise primary/secondary alcohols (I know it's not the catalyst but I tend to forget this one as well

The sulphuric acid one's the one I can't remember.

And resources sucks.

For the dichromate ions do you write H+/Cr2O7 -2

or just acidified dichromate ions?