chesmitry sis and trans isomers. EXPERTS PLEASE?

Question

Which of the following compounds can exist as cis and trans isomers ?



a) CH2=CHF


b) CHCl=CH-CH2Cl


c) HClCFCl


d) CBrBr=CH-CH2Cl


e) 3-hexene



please explain how uk now when something is both cis and trans isomer. thanx.

Answer 1

a.) There cannot be a cis or trans isomer, because the position of Florine can be changed merely by rotating the molecule.

b.) There is a cis or trans isomer, because the Cl and the CH2Cl may be on the same side, or on opposite sides.

c.) No double or triple bond, thus is cannot have a cis or trans isomer.

d.) No cis/trans isomer, because on the left, the carbon has 2 Br's - it doesn't matter which side the CH2Cl ends up on, it's on a side with a Br on the other end of the double bond.

e.) Yes, because the carbons on the other end of the double bond may be on the same side, or opposite sides.

f.) To have a cis/trans isomer, there must be a double bond or ring, which restricts rotation, and there both sides of the double bonds must have something different bonded to the double bonded molecule: for example, on a C=C double bond, each side of the C must bond to 2 different groups.