How can I assign relative priorities to the groups or atoms in each of the following: #-CH_2OH#, #-CH_3#, #-H# and #-CH_2 CH_2OH#?
1 Answer
Jun 4, 2015
Step 1: Look at the atoms that are directly attached to the bond.
They are, respectively,
The three
To decide between the three carbon atoms, we must go to
Step 2: Look at the atoms one bond further out.
We list the atoms in order of decreasing atomic number.
- In
#"–CH"_2"OH"# , the bonds directly attached to#"C"# are#"(O,H,H)"# . - In
#"–CH"_3# , the bonds directly attached to#"C"# are#"(H,H,H)"# . - In
#"–CH"_2"CH"_2"OH"# , the bonds directly attached to#"C"# are#"(C,H,H)"# .
Step 3: Look for the point of first difference in each list.
#"-CH"_2"OH"# is priority 1, because#"O"# has the highest atomic number#"–CH"_2"CH"_2"OH"# is priority 2, because#"C"# has a lower atomic number than#"C"# #"-CH"_3# is priority 3, because#"H"# has the lowest atomic number
The order of decreasing priority is