Numbering for Haloalkenes

[Rohan Singhal 2D]

On page 50 of the O-chem textbook, the name given for the line structure at the top right side of the page is E-3-Chloro-4-fluoro-7-methyloct-3-en-5-yne. Why isnt the name E-6-chloro-5-fluoro-2-methyloct-5-en-3-yne? When we compare the numbers the orders for the respective names are:
3,3,4,5,7 and 2,3,5,5,6
When we compare the first numbers of each set, the second naming type has the lower number, and I remember Professor Lavelle saying that we use the name that has the first lowest number. So why is the actual name the other one?

[Samuel Yang]

Here is a website with the priority of functional groups:
http://www.chem.ucalgary.ca/courses/351/Carey5th/useful/nomen.html

The halide (Cl) has the highest priority as a functional group. That is why it must have the lowest number (3) and so you start numbering from the right of the organic compound. In cases where we use the lowest number like Lavelle mentioned, is when there is no priority such as methyl, ethyl and propyl groups (alkanes) in an organic compound. There are all a part of the alkane functional group and no substituent has priority, so you would just use the lowest numbers possible.

Take a look at page 21 in the Organic textbook and so the example C12H24. That should help you discern why we use the smallest number when possible!

[Samuel Yang]

Actually, this is wrong^

Alkenes have higher priority than alkynes in the numbering process so it should have a lower number.