The influence of ionisable groups on the rotatory power of optically active octyl and menthyl esters
Miles, John Bramwell
A parallel between the orienting powers of substituents and their influence on the rotatory power of λ- menthyl and sec-β-octyl esters of ortho substituted benzoates has been established by Rule and his co- workers (loc.cit. ). This has now been ,shown to hold_ for octyl benzoates containing the ionisable substituents OH, NH2, and NMe2 . As is the case with other o- and p-directive groupings these substituents lower the rotatory power of sec-β-octyl benzoate. On ionisation the hydroxyl group becomes more strongly o, p-directive and the rotatory power is so greatly depressed that the sign of the rotation is reversed. The amino and dimethylamino groups, on the other hand, change, on ionisation, from o, p-directive to m-directive groups. In agreement with this, the hydrochlorides of the basic esters have much higher rotatory powers than have the free esters. .The rotatory powers of the octyl p-substituted amino and dimethylamino benzoates are unexpectedly high, but on ionisation they drop to normally high values of the same order as those of the nitro, carboxy, or methoxy derivatives.The effect of substituent groupings on the rotatory rotatory powers of octyl and menthyl benzoates seems to be propagated through space and not through the chain of atoms. If the effect were transmitted through the chain in a similar manner to the way in which the orienting influences are supposed to be propagated according to Robinson, Ingold, or Flürscheim, it should be evident in other positions in the ring as well as the ortho position. We should therefore expect to find. the peculiar o- effect in the para position, but the results obtained confirm those of Rule and MacGillivray in showing that this is not the case. Propagation through space possibly explains also the absence of this influence in the quinaldinic and picolinic esters, in which the nitrogen atom is one degree further removed than in the o-amino esters; and thus resembles the m-compound in so far as space influence is concerned.The sodium alkoxide method of preparing the hydroxy, amino and dimethylamino esters described in this thesis appears to be the most rapid and satisfactory method, yet devised, or obtaining these compounds in the optically pure state. It seems to be the only way or obtaining the anthranilate and p- aminobenzoate from the corresponding acids.In conclusion the writer desires to express his thanks to Dr H. G. Rule for his very valuable advice and interest during this investigation.