chemistry 6.8 - stereoisomerism

Why can’t atoms rotate around double bonds the way they can around single bonds?

Because of how the p orbitals overlap to for pi bonds and they are rigid so don’t bed much. If any single bonds in the molecule they han still rotate

What are stereoisomers?

Have the same structural formula but different arrangements in space. Happens when Bon Cs in C=C have different atoms / groups attached to them

What are Z-isomers?

Same group above / below double bond

What are E-isomers?

Different groups above and below the double bond

How do you use the Cahn-Ingold-Prelog (CIP) rules to work out if an isomer is an E or Z if all the groups attached to the Cs in the C=C are different?

1. compare the atomic numbers of the atoms bonded to the Cs

2. Highest atomic number gets priority (label number 1)

3. If the 2 atoms bonded to the same C are the same you then look further along the chain (e.g if bonded ti one C was CH2CH3 and CH3 the first 3 are the same (CHH) but the its C (12) and H (1) si the first one would get priority)

1. If both the 1s are above / below the double bonds it’s a Z-isomer, if not it’s an E-isomer

What are cis and trans isomers?

Can only call isomers this if the Cs have at least 1 group in common

Cis- same groups located above / below double bonds (e.g H is bonded into both Cs and on both is below the double bond)

Trans- same group bonded to different Cs on different side of the double bond (1 above and 1 below)