Triply bound

As anticipated for a conjugated multiple triply bound structure, it is extremely endothermic (AH°f (g) +626.4 kJ/mol, 8.22 kJ/g), and may decompose explosively to carbon powder and nitrogen. When burnt in oxygen a flame temperature exceeding 4700°C is attained [1], and it ignites in air at 130°C [2[. It is potentially explosive in the pine state or in cone, solutions, but is fairly stable in dilute solution [3[. It rapidly polymerises with water, weak bases, alcohols, etc. [2[. 

Fig. 6.2-18 shows the first and second overtone regions of C- H stretching modes in the near-infrared spectra of three 1-alkynes (CsHg, CeHio, C7H12, from bottom to top). The C-H stretching modes of triply bound C- H groups are shifted to still higher wavenumbers. The first overtone is observed around 6525 cm (Fig. 6.2-18a), and the second overtone is found around 9637 cm (Fig. 6.2-18b). These absorptions are thus distinctly set off from those of C-H groups whose carbon atom is involved in single or double bonds.

Triply bound Mo dimers yield tetramers when F, Cl, or Br replaces alkoxides as in reactions (i) and (j) ... 

Each of the tetramers has a unique structure X = Cl yields an Mo4( <-OPr-i)8 square with four Mo-Mo distances of 238 pm X = Br produces a M04 butterfly with five Mo-Mo distances near 250 pm and one open side (329 pm) X = F gives a pair of triply bound dimers (Mo-Mo 226pm) linked through F bridges (Mo Mo 375 pm) . Other tetramers best considered as linked dimers are discussed in 92.9.5. 

Trivalent fragments such as RC= (carbyne or alkylidyne group) and N= (nitride) that are triply bound to a metal are three-electron donors. 

A characteristic feature of this mechanism is the substitution pattern in the product. The entering nucleophile need not always enter at the carbon to which the leaving group was bound, since it can add to either of the triply bound carbons. 

The much slower rearrangement of alkynyl and cyano substituents can be attributed to the reduced stability of the intermediate derived by cyclization of the triply bound substituents. 

Hydrazoic acid (HN3) is another member of the set of 16 valence electron 1,3 dipoles. As with both NNO and HCNO, HNNN has a hypervalent central nitrogen atom that is both doubly and triply bound to its neighbouring atoms. The calculated properties of the neutral, protonated and metal ion complexed hydrazoic acid are tabulated in Tables 2, 3 and 33-36. The photochemistry and detonation properties of HN3 have been of particular interest. 

In the table of bond energies separate values are conveniently listed for singly, doubly, or triply bound atoms, for O in C==0, for 0 in C—0—C, and so on. 

Nitriles = Compounds having the structure RC = N thus, C-substituted derivatives of hydrocyanic acid the suffix nitrile denotes the triply bound = N atom, not the carbon atom attached to it. 

In some cases, two types of proton-binding sites are considered, such as in the case of goethite, where singly and triply bound surface OH have been distinguished by Rahnemaie, Hiemstra, and Van Riemsdijk (2006), using the 1-pK model for each, namely... 

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