To investigate the relative stability further among the three enolate rotamers, interaction regions were calculated using the NCIPLOT program and can be seen in Figure . The noncovalent regions in Figure can be identified by the low-density, low-gradient spikes, which are mostly bound by ρ < 0.03 a.u.; this bound was therefore chosen for the visualization of non-covalent interactions. Figure visualizes all the rotamers and their gradient isosurfaces, which allow for a rich visualization of the non-covalent interactions as broad regions of real space, using the ρ < 0.03 a.u. bound for the density. Focusing on the interactions in the non-terminal region of the enolate (i.e., not within the nitrogen heterocycle), the isosurfaces for the Θ min ≈ 50 • rotamer have three attractive interactions: between a slightly positively-charged C β -bonded hydrogen and the negatively-charged oxygen, between a slightly positively-charged methyl-hydrogen and the slightly negatively-charged α-carbon, and a weak attraction between another methyl-hydrogen and the oxygen. Some repulsion is observed also between the aforementioned C β -bonded hydrogen and the former-carbonyl carbon, and between the methyl-and α-carbons, which is to be expected due to their like charges. In contrast, the Θ min ≈ 180 • rotamer only has the attractive and repulsive interactions between the C β -bonded hydrogen and the former-carbonyl group; the CH 3 S group is oriented away from the main body of the warhead, so the other non-covalent interactions between the CH 3 S group and the main warhead are not present in this rotamer. Finally, the Θ min ≈ 310 • rotamer possesses the same non-covalent interactions as the other synclinal rotamer apart from the weak attraction between the methyl-hydrogen and the oxygen, which is due to the conformation of the methyl group with respect to the main warhead. From Figure , it can be seen that synclinal additions are more stable over antiperiplanar due to the magnitude of attractive non-covalent interactions between the CH 3 S group and the warhead. This is in contrast to previous rationalizations, which determine the greater stability of synclinal rotamers to be due to the lone pairs on the sulfur being located further away from the C=C electron density and avoiding repulsive interactions with the lone pairs on the oxygen. The magnitude of non-covalent interactions in the terminal region of the enolate unsurprisingly increases as the warhead size increases. This can be seen in Figure and Figure , where the low-density, low-gradient spikes within the non-covalent interaction regions become denser and the magnitude of the gradient isosurfaces increases, respectively, as the warhead size increases.