Engels enthalpy

Scheme 6.42 Calculated free enthalpies of various states of the isobenzene 162 and its analogues having the CH2 group replaced by a BH group, an N H group or an oxygen atom, according to Engels and co-workers.

The switch from Myers-Saito to Schmittel cyclization occurs with phenyl or bulky groups attached to the alkynyl position of the enyne-allene. Engels compared the Myers-Saito and Schmittel cyclization for the parent reaction with R=H, phenyl, and f-butyl (Fignre 4.15) at B3LYP/6-31G. The activation enthalpy for the Myers-Saito reaction increases from 21.4 kcal mol" when R=H to 26.7 kcal mol" for R=phenyl, and 27.9 kcal mol for R=f-butyl. Conversely, the phenyl group decreases the activation enthalpy for the Schmittel reaction from 29.0 to... 

Figure 3. Formation enthalpies from experiments ( x) (Hultgren, 1963), quantum-mechanical calculations (-I-) (Hackenbracht and Kiibler, 1980) and estimates (o) according to de Boer et al. (1988), as a function of composition for the Ni-Al system (Engell et al., 1991).

Figure 6. Young s modulus as a function of total phase enthalpy (Hultgren, 1963 Engell et al., 1991 Von Keitz and Sauthoff, 1991) at room temperature for the f.c.c. elements Al and Ni (Al) (a) (Lide, 1992), the f.c.c.-ordered NijAl with an Llj structure ( + ) (Davies and Stoloff, 1965 Munroe and Baker, 1988), the b.c.c. ordered FeAl, NiAl and CoAl with a B2 structure (a) (Harmouche and Wolfenden, 1985), and the cubic Laves phases CaAlj, YAlj, LaAl2, NbCrj, ZrCoj and HfCoj with a C15 structure (x) (Shannette and Smith, 1969 Schiltz and Smith, 1974 Fleischer et. al., 1988).

Figure 7. Activation energy of diffusion as a function of total phase enthalpy for Ni, Al, NiAl and NijAl (Frost and Ashby, 1982 Wever et al., 1989 Engell etal., 1991 Von Keitz and Sauthoff, 1991).

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