Where to start counting Winter 2013 final 6A

[004263380]

Why Is the answer to 6A of final 2013 1,5,5,6 tetramethylcyclohex-1-ene and not 2,3,4,4 tetramethylcyclo-hex-ene? I thought that the double bond determines where 1 is and then we start counting based on what gives the 2nd substituent the smallest number.

[ch1995]

1,5,5,6 tetramethylcyclohex-1-ene
2,3,4,4 tetramethylcyclo-hex-ene

^Comparing the #'s above, the first (lowest) numbers for each name are 1 and 2. Since 1<2, 1,5,5,6 tetramethylcyclohex-1-ene is the correct name. When we number the carbons, the double bond does determine where C1 is (C1 has to be one of the carbons involved in the double bond). Then we start counting based on which carbon is closest to a substituent (gives the substituent the lowest number).

[Madison_Moore_1I]

I'm a little confused on why it couldn't be 1,2,3,3.

[Hirmand_Sarafian_2N]

The double bond takes priority and you need to move across it so you have to start at 1 for the double bond and move left

[104469125]

As previously mentioned, the double bond takes priority and you have to move across the double bond. Also, to help figure out why the answer is not 2,3,4,4: If you start counting from the double bond and move left you will get 1,5,5,6 tetramethylcylohexene, instead of 2,3,4,4, tetramethyclyclohexene. When comparing the two, the smaller number "1" indicates that 1,5,5,6 tetramethylcyclohexene is going to be the correct answer.

[Veronica_Giap_1C]

I am still confused, because if you identify the double bond as the 1st carbon and move right, you're still moving across the double bond, and the sum of 2,3,4,4 would be less than 1,5,5,6. I was under the impression that the priority was about the sum of numbers identified, not the 1st of the numbers identified?

[104469125]

Dr. Lavelle told us not to use the sum of the numbers as a reliable way to figure out whether we have the right answer or not. Instead, if you see that there is another way to (correctly) answer the question that will provide you with a lower number in it, then you go with that one. So, in this case because "1" is smaller than "2" we use the name that has the "1" in it. Hope this helped!