Strength, cleavage

Strength, cleavage— The tensile load expressed as force per unit of width of bond required to cause cleavage separation of a test specimen of unit length. 

Not commonly done with wood adhesives but D-1062 (see metal, strength, cleavage) should be applicable with possible modifications to assure stressing the glueline. 

The /-butoxycarbonyl group (Boc, "t-box ) has been eMens vely used in peptide synthesis, and Boc derivatives of many amino acids are commercially available. The customary reagent for the preparation from the amine is t-butyl azidoformate in water, dioxane/water, DMSO, or DMF. The cleavage by acids of medium strength proceeds with concomitant loss of isobutene and carbon dioxide (L.A. Carpino, 1957, 1973 see section 4.1.2.2). 

Some of the evidence indicating that alkyl substituents stabilize free radicals comes from bond energies The strength of a bond is measured by the energy required to break It A covalent bond can be broken m two ways In a homolytic cleavage a bond between two atoms is broken so that each of them retains one of the electrons m the bond... 

The strength of their carbon-halogen bonds causes aryl halides to react very slowly in reactions in which carbon-halogen bond cleavage is rate determining as m nude ophilic substitution for example Later m this chapter we will see examples of such reactions that do take place at reasonable rates but proceed by mechanisms distinctly dif ferent from the classical S l and 8 2 pathways... 

The mechanism for photodegradation at short wavelengths is generaUy beUeved to be initiated by the photolytic cleavage of the amide bond (eq. 17), which has the lowest bond strength in aUphatic polyamides (220 kj/mol (53 kcal/mol))... 

The following carbamates have seen little use since the preparation of the first edition of this book they are listed here for completeness. For the most part, they are variations of the BOC and benzyl carbamates, with the exception of the azo derivatives, which are highly colored. The differences between them are largely in the strength of the acid required for their cleavage. 

This group is stable to TEA and morpholine in pyridine at 20°. It is cleaved by oxidation with MCPBA followed by elimination with TEA in Pyr, 10 min, 20°." The rate of cleavage is proportional to the strength of the electron-withdrawing group on the phenyl ring. ... 

It is not very difficult to appreciate that if polymer molecules are aligned as in Fig. 18.10 then a much higher tensile strength will be obtained if a test is carried out in the X-X direction as opposed to the Y-Y direction. It is also not difficult to understand why such a material has a lower impact strength than a randomly coiled mass of molecules (Fig. 18.10) because of the ease of cleavage of the material parallel to the X-X direction. 

The replacement of the O—H O bridges with BF2 of BPh2 may affect both the complex geometry [178] and the electron density at the central metal ion [184], providing the opportunity of adjusting the Co—C bond strength towards homolytic cleavage, which is currently accepted to be the first step of the reactions catalyzed by the vitamin B12 coenzyme [185]. 

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