The compound with CAS 108 - 59 - 8 is dimethyl maleate. As a reliable supplier of CAS 108 - 59 - 8, I'm here to share with you its spectroscopic characteristics. These spectroscopic features are crucial for identifying, analyzing, and understanding the compound's structure and properties, which are essential for various applications in the chemical industry.
Infrared (IR) Spectroscopy
Infrared spectroscopy is a powerful tool for analyzing the functional groups present in a compound. For dimethyl maleate, several characteristic peaks can be observed in the IR spectrum.
The carbon - oxygen double bond (C = O) in the ester groups of dimethyl maleate gives rise to a strong absorption peak around 1730 - 1750 cm⁻¹. This peak is a signature of the ester carbonyl group and is very prominent in the IR spectrum of dimethyl maleate. The stretching vibration of the C - O single bond in the ester linkage appears in the region of 1000 - 1300 cm⁻¹. Usually, there are multiple peaks in this area due to different C - O stretching modes.
The C = C double bond in the maleate structure also shows an absorption peak. The stretching vibration of the C = C bond typically occurs around 1620 - 1680 cm⁻¹. However, the intensity of this peak may be relatively weaker compared to the carbonyl peak because the C = C bond in dimethyl maleate is in a conjugated system with the carbonyl groups, which affects its absorption characteristics.
The C - H stretching vibrations of the methyl groups in dimethyl maleate are observed in the region of 2850 - 3000 cm⁻¹. The symmetric and asymmetric stretching modes of the C - H bonds in the methyl groups contribute to the peaks in this area. The out - of - plane bending vibrations of the C - H bonds attached to the C = C double bond can be found in the region of 600 - 1000 cm⁻¹, which can provide information about the substitution pattern of the double bond.
Nuclear Magnetic Resonance (NMR) Spectroscopy
¹H NMR
In the ¹H NMR spectrum of dimethyl maleate, the protons of the methyl groups attached to the ester oxygen atoms appear as singlets. The chemical shift of these methyl protons is typically around 3.7 - 3.9 ppm. This is because the electron - withdrawing effect of the carbonyl group in the ester linkage deshields the methyl protons, causing them to resonate at a relatively downfield position compared to normal alkyl protons.
The protons on the C = C double bond of dimethyl maleate are in a cis - configuration. They give rise to a characteristic pattern in the ¹H NMR spectrum. The chemical shift of these olefinic protons is usually around 6.2 - 6.4 ppm. The coupling constant (J) between the two olefinic protons in the cis - configuration is relatively small, typically in the range of 10 - 12 Hz. This coupling constant value is different from that of the trans - isomer, where the coupling constant between the olefinic protons is larger, around 14 - 16 Hz. This difference in coupling constants can be used to distinguish between the cis and trans isomers of maleate derivatives.
¹³C NMR
In the ¹³C NMR spectrum, the carbonyl carbons of the ester groups appear at around 165 - 170 ppm. These carbon atoms are highly deshielded due to the electronegativity of the oxygen atoms in the carbonyl and ester linkages. The olefinic carbons of the C = C double bond are observed in the region of 120 - 140 ppm. The carbon atoms of the methyl groups attached to the ester oxygen atoms resonate at around 50 - 55 ppm.
Ultraviolet - Visible (UV - Vis) Spectroscopy
Dimethyl maleate has a conjugated system consisting of the C = C double bond and the two carbonyl groups. This conjugated system gives rise to absorption in the ultraviolet region. The π - π* transition of the conjugated system results in an absorption peak in the UV spectrum. The maximum absorption wavelength (λmax) of dimethyl maleate is typically around 220 - 230 nm. The molar absorptivity (ε) at this wavelength is relatively high, which indicates a strong absorption of light in this region. The presence of the conjugated system allows dimethyl maleate to absorb UV light, and this property can be used for quantitative analysis and detection of the compound in solution.
Mass Spectrometry (MS)
In the mass spectrum of dimethyl maleate, the molecular ion peak (M⁺) appears at m/z = 144, which corresponds to the molecular weight of dimethyl maleate (C₆H₈O₄). However, the molecular ion peak may not be very intense in the mass spectrum because dimethyl maleate can undergo fragmentation easily.
One of the common fragmentation pathways is the loss of a methoxy group ( - OCH₃). This results in a fragment ion with m/z = 113. Another possible fragmentation is the cleavage of the C - C bond adjacent to the carbonyl group, leading to the formation of various fragment ions. The analysis of the fragmentation pattern in the mass spectrum can provide information about the structure of dimethyl maleate and help in its identification.
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References
- Silverstein, R. M., Webster, F. X., & Kiemle, D. J. (2014). Spectrometric Identification of Organic Compounds. Wiley.
- Pavia, D. L., Lampman, G. M., Kriz, G. S., & Vyvyan, J. R. (2015). Introduction to Spectroscopy. Cengage Learning.
