Recent period

Class meetings are three times weekly, two hours of lecture and one hour for group discussion. Text material includes a basic reference. World Resources 1990-91 (World Resources Institute, Oxford University Press, 1990), and supplemental references provided from time to time, including available GCI modular materials, articles from recent periodicals, and news items from the daily press. 

Quantum mechanics was the dominant theory in chemistry even before the advent of electronic computers. The conventional date for the beginning of this period may be fixed at 1927 with the publications of the Heitler and London paper on hydrogen molecule [3]. The growth of theoretical chemistry (or better, theoretical quantum chemistry) between 1930 and 1960 (thirty years, again, as for the last period) has followed a research programme different from that accepted in the most recent period. 

U3Og). The concentration during the period 400-300 M years occurs in marine black shales, while that in the 300 M years to recent period is accounted for by sedimentary-type deposits, an important example being the Colorado Plateau deposits of USA. 

The fact that tetrazolo[l,5- ]pyridine reacts with phosphines - via ring opening to the valence bond isomer azide -to give a phosphorane has been long recognized. Some novel applications of this transformation have been published during the recent period. The fused tetrazoles subjected to this reaction, the resulting phosphoranes, and the literature sources are summarized in Table 4. 

Fairly limited amounts of novel information on the reactivity of partially conjugated tetrazolo[ 1,5-tf jpyridincs was published during the recent period, and all by Quast etal. <1997LA671, 1998EJ0317>. The most important aspects of the results are shown in Scheme 16. 

Some more or less routine transformations with side chains of tetrazolo[l,5-tf]pyridine or its benzologue have also been published during the recent period, and these results are shown in Scheme 19. 

Further ring systems that have not been reported during the recent period can be found in CHEC-II(1996) <1996CHEC-II(8)421>. 

Two results in the area of the ring system of this subsection appeared during the recent period of time the chemical transformations are shown in Scheme 59. 

Since the publication of some results on this subject as reviewed in CHEC(1984) and CHEC-II(1996) <1984CHEC(5)860, 1996CHEC-II(8)465>, no new results have appeared during the recent period of time. 

The synthetic pathway to tetrazolo[l,5-tf]pyrimidines starting from 5-amino-tetrazoles has already been discussed in CHEC-II(1996) <1996CHEC-II(8)465>. During the recent period of time, several modifications of this approach have been described. The obtained products - among them some partly saturated derivatives - and the applied reagents as well as yields and references are summarized in Table 9. 

Because of the numerous possibilities of arrangements of heteroatoms in the ring systems covered in this chapter, a substantial amount of literature data appeared during the recent period. The ring systems discussed here are shown in Scheme 1. 

Three triazole-fused oxadiazines have been synthesized during the recent period, as shown in Scheme 19. 

During the recent period of time novel results have been published concerning five ring systems belonging to this chapter. These are summarized below. 

CHEC-II(8)496>, where, unfortunately, the numbering of the title ring system (title of Section 8.20.5.2.) appeared erroneously. During the recent period, new approaches have been found, and they are summarized below (Scheme 10). 

WRITING INKS.—There are few chemical preparations, perhaps none, of whieh tire benefit in civilized life Is so great, or of which the use is so widely extended, as that of common writing ink consequently, there is no compound tire quality of which it is so necessary to inquire into and yet there is perhaps no subject which, up to a comparatively recent period, has been more neglected by chemists. 

Walshaw (2006) in a posting reported the presence of three grains of Eleusine in excavations in an Island off the coast of Africa (Tanzania) and this was dated to a rather recent period. 

Until recently periodic copolymers (consisting of more than two monomers) have been a more or less theoretical domain, treating special kinds of polycondensations rather than polymerizations. Not long ago, donor—acceptor complexes (often zwitterions) composed of two or more compounds (monomers) were discovered, homopolymerizing as a whole to yield periodic polymers. 

These figures are average numbers, but you can do the same work for a more recent period. 

The recent period of rapid progress began with the discovery of the sulfa drugs by G. Domagk. In 1935 Domagk discovered that tlu compound prontosil, a derivative of sulfanilamide, was effective in the control of streptococcus infections. It was soon found by other workers that sulfanilamide itself is just as effective in the treatment of these... 

---