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Microsoft word - szerves kémia - mintafordítás.doc

THEORY OF ORGANIC CHEMISTRY
(by dr. SZÁNTAY Csaba)
3rd, Supplemented Edition
MŰSZAKI KÖNYVKIADÓ, BUDAPEST, 1984
Dr. DEÁK Gyula, University Lecturer, PhD. of
Chemical Sciences
Contributed to the samples:
Dr. MAJOROS Béla, Cert. Chem. Eng., Univ. Assist.
Lecturer,
Copyright:
Dr. SZÁNTAY Csaba, Budapest, 1970
ISBN 963 10 0682 4 (3rd /revised/ edition)
ISBN 963 10 5757 7
Editor in charge: BOROSS Anna, Cert. Chem. Eng.
The most the cybotactic region differs from the pure solvent, the more difficult it is to draw conclusions from the macroscopic properties of the solvent regarding the part it plays in the course of the reaction. Therefore, the solvent must, as a rule, be considered as the complex of molecules. From the point of view of a chemist involved in organic chemistry solvents should be grouped into b) apolar or less polar aprotic solvents, Important solvents to be classified to fall in Group “a” are for example, water, alcohol, amines carbon cads, etc. These substances have nucleophil and electrophil properties at the same time. By their mobile hydrogen they solvate anions very markedly, as a rule by the creation of a hydrogen Thanks to the abilities as donor of their self- standing electron pair, they are capable, at the same time, of solvating cations, too., e.g., If this bi-directional solvating capability is coupled by considerable polarity and a high dielectric constant, then the solvents in Group “a” can greatly contribute to spontaneous ionization, that is, a reaction of SN1 type. This substances, as a rule solvate, themselves, that its, they are composed of associates bound by Group “b” contains the majority of carburetted hydrogen and chlorinated solvents. Within this group we can make further distinctions in view of the intensity of nucleophil property. Ether, dioxin, tetra hydrofuran, (THF), etc. belong to the category of comparably intensely nucelophil The dipolar – aprotic solvants of Group “c” are an extremely interesting and important group of solvents. The hydrogen bound to a carbon atom in them separates, as a rule, very difficultly: if these solvents are to react with D2O, they do not exchange it at all, or if yes, then very slowly with deuterium. The difference in between them and Group “b” is, that their dielectric constant is bigger than appr. 15D. We make this voluntary separation as the aggregations of ions in solvents with smaller dielectric constants are so big, that it is very difficult to examine the behaviour of the individual ions separated in solvent shell. The most important dipolar – aprotic solvent are as follows: Dimethylformamid (DMF), Dymethyl- acetamide (DMAC), Acetone, Nitromethene, Nitrobenzene, Acetonitrile, Benzonitrile, Sulphur- Dioxide, Prophylene-Carbonate, N-Methyl-2- pirrolidone, and Tetramethyl-carbamide. Sulfolane and Dimethylsulfon melting/dissolving above ambient temperature are also used many times. The main properties of some solvents are The most frequently used dipolar – aprotic solvents are DMF, DMAC, DMSO and Acetone. the reason for their popularity is that they are cheap We can make another distinction within Group “c” (Meszmer, A.), on the basis whether a solvent is intensely nucleophil (intensely alcaline) such as for example DMSO or only slightly, as e.g., Aceto- As a rule, SN2 type reactions, especially those between anions and neutral molecules, are much quicker in dipolar – aprotic solvents than in rearrangments are slower than in the solvents belonging to Group “c” or “a”. The reaction speed independent of the solvent. These simple observations, however, can be a help when we want to achieve a poorer product with shorter reaction time, better exploitation rate and the forcing of In the light of our arguments regarding cybotactic region, the dielectric constants of the various solvents summarized in Table 5.1 do not in themselves give any information as to what reaction speed is to expect. Several reactions are several million times quicker in a dipolar – aprotic solvent then in a protic solvent having similar dielectric constant. The polarity of solvents have no exact definition as of yet (65), but based on the assessment of the various factors, protic solvents can, as a rule, be deemed We can find intensely polar solvants in Group “c” they, however, do not help SNI tpye reactions, first of all, as they canot solvate and stabilize the anion breaking lose by a strong hydrogen- bridge. Simultaneously, they better solvate most of the cations, such as Na+, and Ka+ than e.g., considerations can be used for understanding the relationship between the change of polarity and reaction speed within a given solvent type. If a icreaseactivation energy (and reduce reaction speed); if the transitory state is less polar than the starting state of reactants, as the latter gets better solvated in more polar solvent. If we however take it the otherwise: if a solvent is more polar, it shall reduce ctivation energy (in other words: increase reaction speed if the transitory phase is more polar than the starting The effect exerted by the solvent on the SN2 reaction of molecules without polarity leading to their getting ions is demonstrated by Table 5.3 Some physical constants of frequently used
solvents
Group “a”
Group “b”
Group “c”

Source: http://meta-frasi.hu/forditas/szerves_kemia.pdf

Microsoft word - guÍa didÁctica profesor _5_.doc

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