 The trans diastereoselectivity observed results from the reversibility of the initial addition , allowing equilibration to the favored anti betaine over the syn betaine . Initial addition of the ylide results in a betaine with adjacent charges ; density functional theory calculations have shown that the rate @-@ limiting step is rotation of the central bond into the conformer necessary for backside attack on the sulfonium . 
 The trans diastereoselectivity observed results from the reversibility of the initial addition , allowing equilibration to the favored anti betaine over the syn betaine . Initial addition of the ylide results in a betaine with adjacent charges ; density functional theory calculations <a href='been_done' title='1'><mark>have</mark></a> shown that the rate @-@ limiting step is rotation of the central bond into the conformer necessary for backside attack on the sulfonium . 
Da trans diastereoselectivity observed results from tdareversibility of the initial addition , allowing equilibration to the favored anti betaine over the syn betaine . Initial addition of the ylide results in a betaine witt adjacent charges ; density functional theory calculations done shown dat the rate @-@ limiting step is rotation of thdaentral bond into the conformer necessary fir backside attack on the sulfonium .