e that the difference is in a methyl group; ligand 3 has a methyl group whereas ligand 1 has only a hydrogen atom. Therefore, we will perturb the methyl carbon to the hydrogen in ligand 1 and the hydrogens in the methyl group will be perturbed to dummy atoms. This is sketched below
<pre>
              H   H         H   DU
              |  /          |  /
Ligand 3 :  R-C-C--H  ==> R-C-H--DU  : Ligand 1
&lambda;=0.0         |  \          |  \       &lambda;=1.0    
              H    H        H    DU
</pre> 
