Question

Which one is correct 3 ethyl 2 methylcyclohex 1 ene or 6-ethyl 1-methyl cyclohex 1 ene?

Answer 1

The correct name is 3-ethyl-2-methylcyclohexene.

Explanation:

The structure of your compound is

The alkene carbons must get numbers 1 and 2.

As you saw, you can number around the ring clockwise or counterclockwise.

The rule is "When you can number around the ring in two directions, you choose the direction that gives the lowest numbers at the first point of difference."

Going clockwise, you get the numbers 1,2,3.
Going counterclockwise, you get the numbers 1,2,6.

Clockwise:`color(white)(mmmml)1,2,color(red)(3)`
Counterclockwise: `color(white)(ll)1,2,color(red)(6)`
First point of difference: `color(red)(↑)`

The first number in each set is 1.
The 2nd number in each set is 2.
The 3rd number in each set is different: 3 and 6.

We choose the clockwise numbers, so the name becomes

3-ethyl-2-methylcyclohexene

We do not include the number 1 in the name.