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IR, MS, UV, NMR SPECTROSCOPY - PDF
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Embeds 0 No embeds. No notes for slide. B mistry a handbook of spectroscopic data chemistry 1. Mistry B. Science College. Narayan Niwas. Mehra Offset Printers, Delhi. All Rights are Reserved. No part ofthis publication may be reproduced. Responsibility for the facts stated.
The Publisher bears no responsibility for them, whatsoever. Contents 1. Ultraviolet Spectroscopy 1 2. Infrared Spectroscopy 26 3.
Proton Magnetic Resonance Spectroscopy 64 4. Be NMR Spectroscopy 99 5. Mass Spectrometry 6. To be able to use this table, one must first learn to recognize different types of dienes, conjugations, double bonds, etc. A cyclic diene; for example, cyclohexadiene, cyclohepta 1,3- diene, etc. A semicyclic diene; one ofthe double bonds forms part of a ring and the other is exocyclic, or outside the ring. When only one ofofthe two Sp2 hybridized carbons of a double bond is a part of the ring under 6. A homoannular diene is one in which the two double bonds are conjugated and are in a single ring.
Note that both double bonds are exocycIic to ring B. A heteroannular diene is a conjugated system in which the two double bonds belong to two different rings. However, these double bonds are also exocycIic, one of them being exo- to ring A and the other exo-to ring B. Table 1. A simple example of this is 1,2 dimethylene cyclohexane, which gives a strong UV band at Amax nm E 10, which is quite different from the calcualted value.
Polyenes : The above rules Table 1. However, for systems ofextended conjugation, such as those found in carotenoid pigments, Fieser and Kuhn have suggested equations to calculate the basic Amax and Em.. In the case ofcyclic compounds, the ethylenic double bonds conjugated with the carbonyl may be homoannular or heteroannular.
Their spectra show considerable resemblance. In fact, the presence or absence of certain features in UV spectra, such as a low intensity band known as a fine structure band at or about run, is often used to detect the aromatic character of an unknown substance. Benzene Chromophore The simplest aromatic compound is benzene. This is called a primary band. Benzene exhibits a low intensity band at nm Emax Known as a secondary or fine- structure band , with a series offine-structue bands between and nm. With polar substituents, e. These two types oftransfer can be expressed as shown below: Chromophore substitutents: Auxochrome substituents: Table 1.
Let us now apply the rules in Table 1. Dienes 1 Abietic acid Basic heteroannular diene Exocyclic double bonds 1 x 5 Substituents R 4 x 5 Calculated Amax Observed nm 05nm 20nm nm nm [Chromophore is shown by heavy lines; numbers indicate substituents. Polyenes 4 In compounds containing both homoannular and heteroannular double bonds, the diene system which requires least energy for excitation i.
H nmr splitting rules
Enones 1 Cholestenne 2 Cholesta-2,4-dien Six-membered cyclic a-diketone known generally as diosphenols, exist in solution largely in the enolised form. In strong alkaline solution the absorption shifts to about 50 nm to longer waves, due to the formation ofthe enolate ion, to enable diosphenol structures to be characterised. Ultraviolet Spectroscopy 13 However, in the case of acetyl acetone agreement with the calculated wavelength nm is indifferent.
This may be due to the fact that the strong internal hydrogen bond forces the carbonyl group and the double bond into a configuration different from that which is present in cyclic structures, e. Quinones represent a-, or vinylogous a- diketones.
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The spectrum of p-benzoquinone is thus found to be similar with that of a typical a, f -unsaturated ketone with the strong K-band appearing at nrn and a weak R-band near nm. Aromatic carbonyl compounds o 1. II HO"'-.
go This table has been successfully used with disubstituted compounds when the following rules are used: I. Para substitution: a. Both groups are either electron donating or electron withdrawing: Only the effect of the group causing the larger shift is used. For example, the "-max ofp-nitrobenzoic acid would be expected to be the same as that of nitrobenzene, - One group is electron donating and the other electron withdrawing: The shift in the primary band of such a disubstituted benzene is usually greater than the sum ofthe shifts caused individually by the two groups.
Such large shifts in p-disubstituted benzens are attributed to interaction resonance, as illustrated below: Ultraviolet Spectroscopy 15 2. Ortho and Meta substitution: The shift effects are additive. Aniline 13, Shift Ultraviolet Spectroscopy 19 Spectra of nonbenzenoid aromatic hydrocarbons show considerable resemblance to spectra ofbenzenoid compounds, Tropolone and its derivatives show absorption in the region - nm Emax ca 30, and - nm Emax ca 8, ; the latter absorption is characterized by the group of fine structure bands typical of aromatic systems. Qtropolone HO 0 Azulene and its derivatives have complicated spectra consisting of a number of relatively intense bands throughout most of the ultraviolet region up to nm and a number ofrelatively weak bands throughout most ofthe visible region - nm.
As a consequence of the latter, azulene and most of its derivatives are blue. Exercises and problems: 1 Explain the differences in the electron spectra of compounds 2 and 3 compared to compound 1 I. Ultraviolet Spectroscopy 21 1 3 Which structural features may produce a bathochromic or a hypso- chromic effect in an organic compound.
Can you suggest an explanation for the brightening action? Biphenyl K-Band, t.. Which are separated by glc. How UV spectroscopy and application of Woodward-Fieser rules will help to identify the products. GO CO co co While in compound 2 this conjugation cannot be complete owing to the methyl group at the ortho position. A hypsochromic shift blue shift may be caused by a change ofthe medium or by such structural changes like removal ofconjugation.
Therefore band is observed at 4 I 5 nm in 0. Biphenyl thus shows a very intense absorption band at nm K-Band. Biphenyl derivatives with bulky substituents in the ortho positions are more stable in twisted conformations than in the planar conformation, which suffers serious non-bonded compressions from the juxtaposed substituents.
The loss ofconjugation in the twist conformation of2, 2-dimethylbiphenyl is reflected in its UV spectral data, which now structurally is like two moles of o-xylene. Ultraviolet Spectroscopy 25 II It will largely exist in the enolic form as revealed by the observed "-max nm Emax 9, which matches with the Cal. On acetylation the spectrum is restored to that calculated for the system now with OAC in the a-position.
Further confirmation will come from the measurement ofthe spectrum ofthe enolised form in alkaline solution which will show ; , the expected bathochromic shift ofsome 50 nm, i.
Infrarred Spectroscopy 27 Table 2. Alkanes -CH3 C-H str. C-H str. C-H def.
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