Question

Spectroscopy 1. What is the relationship between the infrared spectrum and the molecular structure in the structural determination of organic compounds by means of the correlation tables? 2. How does the interaction between the UV-Vis radiation energy and the material occur? 3. How are electronic removals carried out according to their different types of transition? 4. Indicate the absorption maxima of the most common chromophores and the factors that determine their displacements: the conjugation and the solvent. 5. How is the molar absorption coefficient (å) calculated from the UV / Vis spectrum and the Lambert-Beer Law? 6. Define and identify the following concepts in a mass spectrum: base peak, molecular ion, peak (M + 1, M + 2). 7. How is the presence of chlorine, bromine, sulfur and nitrogen in an organic compound denoted by its mass spectrum?

Answer 1

1. IR spectroscopy plays a major role in determining structure of different organic compunds. By checking the correlation table it is possible to identify the peak arised in the spectra is for which functional group, or unsaturated groupings.Further compounds having same functional groups can also be distinguished with the help of fingerprint region of IR (below 1500 cm^-1). IR successfully distinguishes between the types of hydrogen bonding and also between geometrical isomers of an organic compound. All these we can have by comparing the IR spectra of unknown compound with the correlation table data of different stretching and vibration bands of organic compunds.

2. UV vis spectroscopy is titled electronic spectroscopy, since it involves the promotion of electrons (, , n electrons) from the ground state to the higher energy state. Since the energy levels of a molecule are quantised, the energy required to bring about the excitation is a fixed quantity. Thus electromagnetic radiation with only a particular value of frequency will be able to cause excitation. If the radiation of desired frequency is passed on the sample of the substance, energy will be absorbed and electrons will be promoted to higher energy state. Transitions occur resulting in the formation of bands.