axial chirality, 135 axial (equatorial), 135 axialite in polymer crystals , 136 axis of helicity, 136 aza-di-π-methane rearrangement, 136 azacarbenes [obsolete] , 137azanes, 137 azenes [obsolete] , 137 azides, 138 azimines [obsolete] , 138 azines, 138 azinic acids, 138 azlactones, 139 azo compounds, 139 azo imides, 139 azomethine imides, 140 azomethine oxides, 140 azomethine ylides, 140 azomethines, 140 azonic acids, 141 azoxy compounds, 141 azylenes [obsolete] , 141 β-cleavage in mass spectrometry, 141 β-decay, 141 β-particle, 142 back donation, 142 back electron transfer, 142 back extraction, 142 back scatter coefficient in in situ microanalysis , 142 back scattered electrons (BSEs) in in situ microanalysis , 143 back washing [obsolete] , 143 backbone, 143 backflush, 143 background concentration (level) in atmospheric chemistry , 143 background mass spectrum, 144 background of a radiation measuring device , 144 background radiation, 144 backscatter, 144 baffle chamber in atmospheric chemistry , 145 bag filter in atmospheric chemistry, 145 baghouse in atmospheric chemistry, 145