Skeletal formula of a general <a href="https://en.wikipedia.org/wiki/Carboxylic_acid" class="extiw" title="en:Carboxylic acid">carboxylic acid group</a> (RCOOH)
<a href="//commons.wikimedia.org/wiki/User:Benjah-bmm27" title="User:Benjah-bmm27">Ben Mills</a>
Own work  using: ChemDraw / Photoshop