Wikipedia:Reference desk/Archives/Science/2021 December 24

= December 24 =

4-Nitrobenzyl bromide and 1-methyl-4-(4-nitrobenzyl)piperazine, which is more polar
Structure: And is there any method to calculate the polarity of molecules?
 * 1) 4-nitrobenzyl_bromide_structure.png
 * 2) 1-methyl-4-(4-nitrobenzyl)piperazine_structure.png
 * --Leiem (talk) 17:53, 24 December 2021 (UTC)
 * Here's a WikiHow:
 * Here's a YouTube video:
 * —2603:6081:1C00:1187:9D35:4EEF:98A2:ACEC (talk) 23:11, 24 December 2021 (UTC)
 * The question seems to be not "is it polar?" (obviously it is, it's not symmetric) or simply "which end of the dipole is which?", but calculating how strong the diple is. And that requires knowing the molecular conformation, which the simplified wikihow/videos do not address. The benzyl-bromide case only has one real degree of freedom, so it shouldn't be hard to calculate; the piperazine has two and they might depend on solvent effects...getting harder. DMacks (talk) 16:19, 25 December 2021 (UTC)
 * What if the piperazine ring has a chair conformation? --Leiem (talk) 03:16, 29 December 2021 (UTC)
 * My starting assumptions were that the nitro was reasonably coplanar with the benzene (and not a detail of difference between the two) and that the piperazine was chair with both the methyl and benzyl equatorial. Googling tells me the low-energy conformations of the parent benzyl halides PhCH2X is with the C–Br penpendicular to the benzene ring except for when X=F. So the main unknown is the rotation of the N–Cbenzylic bond. DMacks (talk) 10:16, 31 December 2021 (UTC)