In addition to searching for articles, SciFinder also allows you to draw and download chemical structures. Register for a free account at https://scifinder.cas.org/
registration/index.html?corpKey=1C760952-86F3-5055-1D62-2ACEBD3FF208
Free software download for students after you register for an account.
You can also use non-chemistry tools for rough mockups, such as Microsoft Word or Adobe Illustrator. There are other more advanced drawing software online, often requiring a paid license.