DFT calculations have been performed to compare metathesis of olefin, diene, and arene substrates catalyzed by a 2nd generation Ru(SIMes)-based complex. A large screening of modified substrates has been performed with the intention to explore the energetic gaps between acyclically conjugated alkenes and arenes in metathesis processes. The results are analyzed through the effects of conjugation vs. aromaticity, as quantified by the HOMA and NICS aromaticity indices, as well as the effects of non-covalent interactions between coplanar rings and/or any ring with functional groups nearby.