Assigning Cahn-Ingold-Prelog priority numbering rules for 2 groups

Question

I was asked to draw the perspective formula of

$$\ce{(3R,4R)CH2=CH-CH(CH3)-CH(CH3)-CH2-CH3}$$

Then I had to assign priority between the two groups:

$$\ce{-CH=CH2}$$ and $$\ce{-CH(CH3)-CH2-CH3}$$

Actually, they are bonded to the same atoms until the end of the first group, but one of them should have priority over the other. Can please someone help?

Answer 1

When you've reached the end of your first group (after resolving the double bond), you're next comparing no atom (on the ghost C connected to C2) to a hydrogen atom (on the 4-methyl group), and any atom has a higher priority than no atom, so your second group gets the higher priority.