title: How to add dynamic property in c#
body: <p>I want to convert my model to JSON in this format,</p>
  
  <pre><code>var json = JsonConvert.SerializeObject(new { [item.Key] = new { List = item.ToList() }});
  </code></pre>
  
  <p>How to make this (<strong><em>item</em></strong> is <code>IGrouping&lt;string, object&gt;</code>)</p>