Question

How many constitutional isomers of continuous-chain heptenes exist?

Answer 1

@vocaloid

Answer 2

@tranquility

Answer 3

continuous-chain heptenes: so 7 carbons in a chain, with 1 double bond. how many ways can you place the 1 double bond to create unique isomers?

(no, it's not 6 - remember to consider whether the isomer is unique or not)

Answer 4

2?

Answer 5

I'm not sure how to do this or why we are learning this. This is a physical science for educators' class and I want to teach elementary school so yeah.

Answer 6

I said 4 in a previous answer, it is wrong.

Answer 7

@vocaloid

Answer 8

draw a chain of carbons 7 carbons long, numbering them 1-7

for our first isomer, we can draw the double bond between carbons 1-2

Answer 9

repeating this logic, we can draw

- a second isomer, with the double bond between C2 and C3
- a third isomer, with the double bond between C3 and C4

now, you might be tempted to go and draw another isomer between C4 and C5 like this:



however, remember that molecules are 3d objects that can rotate in free space. if we flip this around, you'll realize that this is identical to the isomer w/ the bond between C3 and C4

continuing this logic, double bond between C5 and C6 is the same as C2-C3, and a double bond between C6 and C7 is the same as the first isomer (between C1 and C2)

thus, there are only 3 unique isomers.

Answer 10

hm, if they want you to consider multiple double bonds - gimme a second

Answer 11

Thank you! Can you help me with the second part of the question?

Answer 12

It's 3

Answer 13

oh good that makes our life much easier

now, we number alkenes (that's what we call carbon chains with double bonds) so that the double bond gets the lowest number.

in the first isomer we drew, we put the double bond at carbon 1, so the first isomer is 1-heptene

following this logic, the next isomer has a double bond at carbon 2, making the second isomer 2-heptene and the third isomer 3-heptene

now, they only want you to consider one double bond for the entire compound, so you want the 1 2 and 3 heptenes that only have 1 double = bond.

Answer 14

Thank you! For this last problem of this chapter, I know there are 2 isomers based on the last question. Would it be 1 and the second 2?

Answer 15

yup perfect

Answer 16

It said it was wrong apparently. It's okay I got an A on the hw still. Again, why I need to know this I will never know.

Answer 17

oh I think I misinterpreted your answer ;-;

it should be the first and second one from the list. 1-heptene and 2-heptene only have 1 double bond each (if we had multiple double bonds we'd have to name each double bond)

Answer 18

ohhhh that's okay