The 0.r.d. curves of ca. 40 carotenoids have been measured, chiefly in dioxan, over the range 400-200 nm. The chromophore in all cases is a conjugated polyene system which is perturbed by one or two chiral end-groups.The curves are analysed in terms of the simple additivity of the effects of end-groups, and the absolute configurations of several compounds have been provisionally assigned.MANY carotenoids contain one or more asymmetric carbon atoms, but little information is available concerning the absolute or relative configurations of these centres. Capsanthin (1) has been degraded to the acid (2) which on further oxidation, gave (-)-camphoronic acid (3),2 also obtained from (+)-camphor (4) of known 3 absolute configuration. Since the two oxygen functions This paper is Part LXII in the Westfield College series on optical rotatory dispersion, preceding paper, Part LXI, G.

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Soci6t6 suisse de chimie, BBle -Societi svizzera di chimica, Basilea Nachdruck verboten -Tous droits r6servCs -Printed by Birkhauser AG., Basel Organisch-cheniisches Institut der Universitat, Zurich. Organisch-chemisches Institut der Universitat, Bonn.(20. IV. 71)Summary. The chiroptical properties (CD. and ORD.) of four stereoisomeric yohimbanes ( 1 4 ) and the corresponding 17-keto derivatives 5-8 have becn studied. The aromatic and the ketonic Cotton effects have been considered in terms of the appropriate Sector and Octant Rules, respectively. Positively charged nitrogen makes an 'anti-octant' contribution to the ketonic Cottovt effect.The chiroptical properties, the NMR. spectra and dehydrogenation reactions with mercuric acetate together indicate the presence of a C/D-trans-quinolizidine system in all the compounds studied, except those of the pseudo series (3 and 7), in which a C/D-cis-quinolizidine system is present. An explanation of the unexpectedly slow dehydrogcnation of the 3-epi-alio compounds 4 and 8 is suggested.Conformational analysis of the results of equilibration experiments on pairs of 3-epimeric compounds (in both glacial acetic acid at 145" and in K-t-butylate at 211") leads independently to conclusions which agree with those drawn from the physical methods. The great differences between the equilibrium positions of the free bases and the protonated forms are due to the presence in the latter cases of oriented ion pairs R,N+H...-O,CCH, .

U = potential elastic energy stored in the system S = surface energy of the system C = crack length L =length of steel rod The surface energy of the system is given by Eq. 2. The coefficient 2 is necessary SInce two new surfaces are being created. joint and a pivot prevent bending stresses in the rod. A differential thread arrangement permits the rod to advance only 0.012 in./revolution of the driving nut. The axial force in the rod is measured with type F A-50-12 Baldwin Lima Hamilton strain gauges and a BLH type 20 strain gauge reader. Separation of the blocks is measured with a Starrett 656-617 dial gauge. The massive nature and design of the equipment minimize the amount of elastic energy stored in the steel parts as the stress in the rod is increased. This will permit the rock to split under controlled conditions as will become clear later. Fig. 2 shows a sketch of the rock sample during cleavage. Guide slots are cut longitudinally along the rock sample as suggested by Berry.! An initiating slot is also cut across the top of the block to a depth of 1 to 2 in.During cleavage, elastic energy is stored in the flexed beams of rock of length C. If the length of steel rod L is held constant and the crack extends in length, then the elastic potential energy stored in the rock decreases. However, surface energy must be supplied as the crack extends in length. _ Griffith 6 has proposed the following criteria for mechanical stability. The crack will extend as long as the potential energy available is greater than the surface energy required. However, the crack will stop extending when the change in potential energy with change in crack length is just equal to the change in surface energy with change in crack length. See Eq. 1.. a = specific surface energy W =width of cleaved rock • • • (2) :~JL (1) iJUJ iJ C L = ABSTRACT THE EXP ERIMENT AL METHOD Equipment designed to cleave large rock samples is shown on Fig. 1. This equipment consists essentially of two steel blocks cemented toa rock sample and forced apart with a steel rod. A ball Values of rock surface energy (i. e. energy required to form a unit area of new surface) are useful for interpretation of drilling and fracturing phenonema. This paper describes the adaptation of a cleavage technique (splitting of large rocks under controlled conditions) for measuring surface energies. Values of surface energy obtained at room temperature and at low crack extension rates are reported for a variety of sandstones and limestones. Elastic moduli, tensile strengths and compressive strengths of the samples are also reported. The values of Young's moduli (measured in bending) are relatively low, probably because of the low stress levels imposed. Measured values of surface energy are generally higher than anticipated and probably reflect inelastic yielding near the extending tip of the crack.

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