JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css">
<div class="contents">
  <div class="row row-1">
    <div class="col-sm-6">Content Left</div>
    <div class="col-sm-6">Content Right</div>
  </div>
  <div class="row row-2">
    <div class="col-sm-6">Content Right</div>
    <div class="col-sm-6">Content Left</div>
  </div>
  <div class="row row-3">
    <div class="col-sm-6">Content Left</div>
    <div class="col-sm-6">Content Right</div>
  </div>
  <div class="row row-4">
    <div class="col-sm-6">Content Right</div>
    <div class="col-sm-6">Content Left</div>
  </div>
</div>

CSS

.row:nth-child(2n) .col-sm-6:first-child{
   float:right;
}