Room-temperature spectra preparation

Figure 12-31. Absorption spectrum of the MSA cation prepared by oxidation of a chloroform solution 1.07x10 mol/L MSA (dotted) compared to the room temperature spectrum of injected charge carriers in a MSA single-layer LED containing 20% MSA in PSu (solid) (Ref. [96]).

Of the various [20]annulenes prepared 115>116> only one compound has as yet been investigated by n.m.r. This is l,ll-didehydro-[20]-annulene, 24, whose n.m.r.66) indicates the presence of a paramagnetic ring current. The room temperature spectrum is of the mobile type arising from the rotation of two pairs of trans double bonds, which leads to an averaged "symmetrical molecule (a similar case was seen for l,9-didehydro-[16]annulene, 12). When the bond rotation is "frozen out at — 80 °C, one sees the deshielded inner protons (t —1.60 to —0.45) and shielded outer protons (t4.40 to 4.93) characteristic of an antiaromatic compound. 

On exposure to air, the initially clear orange crystals of the adduct turn cloudy within 1 min as a result of the loss of CS2, and ultimately form a yellow oil. In CS2 solution the adduct decomposes fairly rapidly at room temperature the decomposition products SOCI2, SO2, Sg, and SbCls are already detectable after 10 min. The SO stretching vibrations of Si202-2SbCl5 occur at 940 cm in the infrared spectrum (in CS2) [61]. Free S12O2 has not been prepared yet. 

Figure 21. Room-temperature optical-absorption spectra of various digestively ripened Au colloids prepared by the inverse-micelle method. For comparison, the spectrum of the as-prepared colloid is also displayed. (Reprinted with permission from Ref [49], 2002, American Chemical Society.)...

Figure 27 illustrates a rotaxane of Stoddart et al. [93], in which the axle contains two stations interacting with the cyclobis(paraquat-p-phenylene) bead. Its NMR spectrum at room temperature indicated that the bead moves back and forth like a shuttle between the stations about 1800 times a second. Stoddart et al. [94,95] prepared a [2]rotaxane containing two bipyridinium units and a crown, as shown in Fig. 28. The shuttling speed of the bead estimated by...

---