1.26

[SaniShabgahi3N]

I got the name correctly; however, I don't understand why there is a E. I know E means that the groups are across from each other. But what groups are identical and across from each other in that alkene?

[feodora_r_3d]

Yes, E means that the atoms or atom groups are on opposite sides of the double bond. In this question, Br and CH2CH3 are opposite of each other, which is why it's E. We compare Br and Ch3Ch2 instead of Ch2Ch2Ch3 because Br gets more priority than the Ch2Ch2Ch3 atom groups.

[Daniel-1G]

So it's not that there are two identical groups that are across from each other but rather that the two highest priority groups are across from each other?