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Conformational studies are all most invariably made by physical methods such as X-ray, electron diffraction dipole moment, micro wave and other spectroscopy measurements.X-ray diffraction is one of the well development methods for the determination of structure of a molecule. Although X-ray diffraction patterns established the conformation of a compound, the utility of a technique is limited because a complication involved in analysis of such patterns and technique provides structural information of a compound only in crystalline state because it is not same in liquid state. In the electron diffraction method the weak molecular scattering which is used to determine the molecular structure, is identified carefully from the strong atomic scattering and campared with the calculated pattern of different possible structures. This method is best applied to the compound in gaseous phase. The dipole moment of a compound may be utilized to estimate the conformational exchanges involved in the compound in solution. The equilibrium constant can be evaluated from the experimental value of the dipolemoment and calculated value of the different conformers. This method is very useful in the study of rotational isomerism. Change of temperature leads to a change in the proportion of the isomers and thus to a change in effective dipole moment. Vibrational, IR and Raman spectroscopy have also been successfully applied to the structural studies. Fundamentaly these methods are based on the determination of symmetry classes of molecules, a correct structure can be picked up by comparing the spectroscopically determined symmetry class of a compound with those of different possible structures of that compound. Microwave spectroscopy is one of the most applied technique for the determination of the conformational barriers, particularly when the energy barriers are less than 5 kcal/mol like those in ethane which can easily be determined from the intensity of rotational absorption bands. During recent years extensive use of high resolution NMR spectroscopy has been made to study the conformational changes in both cyclic and acyclic molecules. Barriers to various rate processes have been determined in the range of 5-25 kcal/mol. Such large barriers include stereoelectrically hindered rotation about single bond and partial double bonds, hindered inversion of atoms like N, S etc. and strained ring inversion. The lower limit of temperature attainably with the available commercial NMR instruments in still too high for appreciable slowing down of the conformational rate processes for system possessing barriers less than 5 kcal/mol. A compound in which the rate of conformational exchanges is considerably slow on the NMR time scale gives rise to the spectra characteristics of all the different conformers present in that compound. But as the rate of conformational exchange are increased by raising a temperature above a certain level. A compound shows only a time averaged spectrum of all the conformers.

The aim of research is overall purpose of conducting the Research. It could be to add to the knowledge in the area, to address an existing gap in the knowledge, to devise and test a solution to an existing problem.

The last 15 years have seen an explosive growth in applications of the Diels-Alder reaction, principally the intermolecular (IMDA) reaction but also the transannular (TADA) version. In this review we present these developments with special emphasis on the stereo chemical concepts and the experimental results and include related theoretical studies.

60 MHz ¹H NMR Spectrum of N¹-diacetyl-N-Aminoimide of Naphthalene-Maleic Anhydride endo and exo Adducts in CDCl₃

(1)                                                                         (2)


(3)                                                                          (4)

This technique involves certain advantages over other physical methods employed for configurational assignments. Experimentally this technique is simple and straight forward & also avoids skeletal rearrangements The testing probe is held directly over the dienyl part of the adduct & provides a clear picture of the cage magnetic envitonments of the endo exo cage moieties of the adducts . Adducts could be utilized for structural assignments. The endo/exo may be helpful in eatablishing the configuration when one comprises the spectral patterns of the two isomeric adducts. But in certain cases one of the isomeric adduct may not be available and then this technique would be more helpful in configurational assignments. The chemical methods used for configurational assignments are quite laborious and gives many side reactions e.g. rearrangements etc., where the identification of the products becomes difficult. Therefore chemical methods may not yield fruitful results regarding the configurational identification

The conformational studies of a series of N¹-(diacetylamino) – imide derivatives of endo and exo adducts of cyclic dienes and maleic anhydride have elegant method of determination of configuration of the Diels-Alder adducts^1-9. Since the N¹-(diacetylamino) imide system assume  a non planar  conformation  about the N-N bond at room temperature. The N¹-(diacetylamino)-imide system could be a sensitive probe when there is a large magnetic asymmetry about the plane of the diene and dienophile linkage, such as adducts of naphthalene and its derivatives with maleic anhydride (1) and (2). In the spectrum (fig. 1) of one of the isomeric adducts (1a), the two acetyl signals are separated by 1.65 ppm appearing at δ0.90 & δ2.55 while in the other (2b) appear at δ2.20 and δ2.33 (δ-.13 ppm). The appearance of the acetyl signal at a very high field could be due to the large expected magnetic anisotropy of the benzo ring in the endo-adduct. Thus (1) was assigned the endo (2) & the exo configuration. The similarty in the chemical shift values of acetyl groups in N, N-diacetyl-N-amino 1,2,3,4 – tetra hydro, 4- ethanonaphthalene – 2, 3- exo dicarboximide (1a)  and (2b) suggested that the magnetic influence of olefinic and ethylenic bridge on the N¹-actyl groups are very much similar, hence it became very difficult to assign the configuration of endo and exo products (3) and (4) on the basis of δ values of N¹ -diacetyl groups.

The aim of this experiment was to explain the stereochemistry of Diels-Alder adduct of N1-diacetyl-N-Aminoimide of Naphthalene-Maleic Anhydride (endo and exo) by conformational and configurational assignments.

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