olefins, 1024 oligo, 1024 oligomer, 1025 oligomer molecule, 1025 oligomerization, 1025 oligonucleotides, 1025 oligopeptides, 1026 oligosaccharides, 1026 one-bond-flip, 1026 one-photon photochromism, 1026 onion morphology, 1027 onium compounds, 1027 open film, 1028 open hearth furnace in atmospheric chemistry, 1028 open-shell systems, 1028 open-tubular column in chromatography , 1028 operational pH cell, 1029 operational pH standard, 1029 operator gene, 1029 operon, 1029 opposing reactions, 1030 optical activity, 1030 optical antipodes [obsolete] , 1030optical density [obsolete] , 1030 optical filter, 1031 optical isomers [obsolete] , 1031 optical multi-channel analyser, 1031 optical parametric amplification, 1031 optical parametric oscillator, 1031 optical purity, 1032 optical resolution [obsolete] , 1032 optical rotation, 1032 optical rotatory power, 1033 optical spectroscopy, 1033 optical yield, 1033 optical-beam error in spectrochemical analysis , 1033 optically active polymer, 1034 optically labile [obsolete] , 1034 optoacoustic spectroscopy, 1034 orbital (atomic or molecular), 1034 orbital energy, 1034 orbital steering, 1035 orbital symmetry, 1035 order of reaction, , 1035 order parameter, 1037 order-disorder transition, 1037 ordered co-continuous double gyroid morphology, 1037 organelles, 1038 organic dye laser, 1038 organically modified silica, 1038 organically-modified ceramic, 1038 organic–inorganic polymer, 1039 organo-, 1039 organoheteryl groups, 1039 organometallic compounds, 1039 organyl groups, 1040 origin of replication (ori), 1040 ortho acids, 1040 ortho amides, 1040 ortho esters, 1041 ortho – and peri-fused (polycyclic compounds), 1041 ortho -fused (polycyclic compounds), 1041 orthokinetic aggregation in colloids , 1042 osazones, 1042 oscillating reaction, 1043 oscillator strength, , 1043 osmolality, , 1043 osmotic coefficient, , 1043 osmotic concentration, , 1044 osmotic pressure, , 1044 osones [obsolete] , 1044 osotriazoles, 1045