[rajm95]

Why is this compound R??
so what i did is placed the priority(1-4) acording to its atomic number.
and i after that i checked that the hydrogen was dashed, and after that, the numbers are neither accomodated clockwise or counter clockwise so... im stuck

[K.z_z]

The priority should be
1) NH2
2) -C(CH₃)₂HS
3) -COOH
4) Hydrogen
 
The reason the -COOH group (Let's called it C3) has lower priority is that the other carbon is connected to a S (let's call it C2), which has atomic number 16.
So the C3 (-COOH carbon) is connected to O,O,O
The C2 is connected to S,C,C
Since atomic number of S is 16, and atomic number of O is 6 , C2 gets priority.  Therefor it is R, not S.

Note that Once one of the 3 atoms the carbon is connected to has higher atomic number, that carbon gets the priority no matter what the other two atoms are.

[rajm95]

The priority should be
1) NH2
2) -C(CH₃)₂HS
3) -COOH
4) Hydrogen
 
The reason the -COOH group (Let's called it C3) has lower priority is that the other carbon is connected to a S (let's call it C2), which has atomic number 16.
So the C3 (-COOH carbon) is connected to O,O,O
The C2 is connected to S,C,C
Since atomic number of S is 16, and atomic number of O is 6 , C2 gets priority.  Therefor it is R, not S.

Note that Once one of the 3 atoms the carbon is connected to has higher atomic number, that carbon gets the priority no matter what the other two atoms are.

thank you very much:) know it makes sense