Liquid HCN is dangerously unstable with respect to trimer formation—that is, formation of (HCN)₃ with a cyclic structure.
(a) Propose a structure for this cyclic trimer.
(b) Estimate the energy of the trimerization reaction using bond dissociation enthalpies (Table 8.8).

Data given in Table 8.8

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TABLE 8.8 H C ZO N O FS Si P S CI Br I N=N N=N Some Average Bond Dissociation Enthalpies (kJ/mol)* Single Bonds 0 F Si 463 565 328 358 485 201 283 146 H C 436 413 346 C=N C=N 0-0 (in 0₂) N 391 305 163 418 945 615 887 498 155 - P S Multiple Bonds C=C C=C 322 - 452 335 565 490 222 201 CI Br 432 366 339 285 192 218 201 284 253 249 293 381 310 326 226 255 242 C=0 C=0 (in CO₂) C=0 347 272 - - - 1 299 213 610 835 745 803 1046 - 201 278 234 184 - 216 208 193 175 151