Abstract: There are provided an optical element that comprises a polymer which has a structural unit derived from a specific dihydroxy compound typified by 2,2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoro propane (bisphenol AF) and in which the relationship between a refractive index nD and an Abbe number ?D satisfies the following formula (I): nD+0.0076×?D?1.78??(I) and that is used for correction of chromatic aberration, and an achromatic lens using the optical element.

Abstract: There are provided an optical element that comprises a polymer which has a structural unit derived from a specific dihydroxy compound typified by 2,2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoro propane (bisphenol AF) and in which the relationship between a refractive index nD and an Abbe number ?D satisfies the following formula (I): nD+0.0076×?D?1.78??(I) and that is used for correction of chromatic aberration, and an achromatic lens using the optical element.

Abstract: Method of producing a bromine compound having an aliphatic unsaturated bond which includes reacting a compound having an aliphatic unsaturated bond represented by the following general formula (1) with bromine:R.sup.1 --O--Ar.sup.1 --Y--Ar.sup.2 --O--R.sup.2 (1)to produce a bromine compound represented by the following formula (2):R.sup.3 --O--Ar.sup.1 --Y--Ar.sup.2 --O--R.sup.4 (2)wherein Ar.sup.1, Ar.sup.2 and Y are the same as defined in the above general formula (1) , and R.sup.3 and R.sup.4 are groups obtained by saturating the unsaturated groups of R.sup.1 and R.sup.2 in the above general formula (1) with bromine, respectively.The reaction is carried out in the presence of a solvent which is inactive in the reaction, and a substantial amount of the heat of reaction is removed from a reaction system by the vaporization of the solvent or bromine. A high-purity bromine compound in high yield which is useful as flame retardant, can be obtained.