Abstract: Optical elements having non-linear optical properties comprising a compound of the formula: ##STR1## wherein E is an electron donorA is an electron acceptor;and W, X, Y & Z are each independently H or any group capable of attachment to the pyrazolyl ring; in which the molecules of the compound are aligned so that the element has a net non-centrosymmetry, a method for their preparation, optical devices comprising such elements, and compounds of formula I.

Abstract: Optical elements having non-linear optical properties comprising a compound of the formula: ##STR1## wherein D is an electron donorA is an electron acceptor;and W, X, Y and Z are each independently H or any group capable of attachment to the pyrazolyl ring; in which the molecules of the compound are aligned so that the element has a net non-centrosymmetry, a method for their preparation, optical devices comprising such elements, and compounds of formula I.

Abstract: Optical elements comprising a non-centrosymmetric compound comprising an electron donor and an electron acceptor linked by a conjugated bridging group, in which the electron acceptor is a nitroso group, in which element the molecules of the compound are aligned so that the element has a net non-centrosymmetry, a method for their preparation, optical devices comprising such elements, and some of the compounds.

Abstract: A process for the preparation of diphenylmethanes and especially of unsubstituted and alkyl substituted diphenylmethanes such as diphenylmethane (DPM) itself and 2-benzyl toluene (OBT) which is an intermediate in the preparation of anthraquinone.The process involves the reaction of a benzene with an .alpha.-chloromethyl benzene in the presence of sulphuric acid and a cationic surfactant, such as a long chain quaternary ammonium salt, or a non-ionic surfactant susceptible to protonation under strong acid conditions, such as an alkoxylated alkyl phenol.

Abstract: Manufacture of o-benzyltoluenes by reaction of a benzyl halide of formula ##STR1## with a compound of formula ##STR2## at 50.degree. to 250.degree. C., one of R and R.sup.1 being methyl and the other H or methyl, and adding the compound II to a mixture of III with a small amount of iron or iron compound.