A simple sentence - which is correct?

[18chineseeng]

The chemical structure of "Compound X" is similar to "Compound Y."

or

The chemical structure of "Compound X" is similar to that of "Compound Y."

Which sentence is the correct one?

Thanks

 

[5jj]

Welcome to the forum, 18chineseeng. :hi:

The second of your sentences is correct, but you will hear some native speakers saying the first.