Some 2-phenylthio-para-substituted cyclohexanones with different oxidation states of sulfur atom were studied by systematic conformational search around C-S bonds using the parametric method 3 (PM3) Hamiltonian. The axial and equatorial regular chair conformations were subjected to calculations and each one produced three rotamers: ϩgauche (؉G), Ϫgauche (؊G), and anti (A). The axial conformations were more populated than the equatorial ones. The para-substituent and sulfur group effects over conformational populations and carbonyl polarizations suggest that the main electronic interaction between sulfur atom and carbonyl group are of repulsive nature in both axial (such as S ϩ C ϩ O) and equatorial (such as S Ϫ CO Ϫ ) conformations. The axial ؉G conformation is the more stable for all compounds, except for (R 2 ,S S )-sulfinyl isomer, because it allows an attractive electrostatic interaction between C-O and S-bond dipoles (such as S ϩ CO Ϫ ). The axial A conformation is the more stable for (R 2 ,S S )-sulfinyl compounds, because the sulfinyl oxygen is at ϪG position near the carbonyl group and an attractive electrostatic interaction (such as O SO Ϫ C ϩ O) can take place. The higher carbonyl polarization and negative charge of carbon C-2 plus hydrogen H-2 of cyclohexanone ring for sulfonyl compared with sulfanyl and sulfinyl compounds, can be explained by a through-space interaction instead through-bond inductive effects.

At the turn of the nineteenth century, a frantic search took place in Minas Gerais for minerals that could prove to be of economic value and thus compensate for the decline in the production of gold and diamonds, the mainstay of the economy in the preceding century. This article addresses the search for new mineral wealth, involving the work of many different explorers and their multidisciplinary research, and particularly the unsuccessful efforts directed to finding and obtaining lead and silver in sizable amounts as two such possible replacements.

SALTPETER: THE STRATEGIC CHEMICAL PRODUCT IN THE PAST OF BRAZIL. Saltpeter demanded for a long-time strategic attention in view of its importance in the form of gunpowder by the governments of many nations. The sources of this mineral in Brazil were almost always associated to the soil in caves, which was extracted because of a limited amount of that precious salt. The first references pointed out that saltpeter was first discovered in the São Francisco basin in regions of the south of the Captaincy of Bahia and in the north of Minas Gerais. Some historical documents show that the Serra do Baldim was the object of intensive mining activities of saltpeter from its caves and the product became the focus of conflicts and left scars on the walls of some limestone caverns.

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Júnior-CRB6/2422 O conteúdo dos artigos e seus dados em sua forma, correção e confiabilidade são de responsabilidade exclusiva dos autores. 2019 Permitido o download da obra e o compartilhamento desde que sejam atribuídos créditos aos autores, mas sem a possibilidade de alterá-la de nenhuma forma ou utilizá-la para fins comerciais. www.atenaeditora.com.br As inúmeras facetas da Espeleologia 1 Capítulo 1 CAPÍTULO 1