A chemist obtained spectral data of pentane-1,5-diamine (C5H12N2) - HSC - SSCE Chemistry - Question 29 - 2021 - Paper 1
Question 29
A chemist obtained spectral data of pentane-1,5-diamine (C5H12N2).
H2N—(CH2)3—NH2
Infrared spectrum
% transmittance
100
Wavenumber (cm−1)... show full transcript
Worked Solution & Example Answer:A chemist obtained spectral data of pentane-1,5-diamine (C5H12N2) - HSC - SSCE Chemistry - Question 29 - 2021 - Paper 1
Step 1
Infrared spectrum
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Answer
In the infrared spectrum, the peak around the wavenumber of 3300–3400 cm−1 corresponds to the N–H stretching vibrations typical of amino groups. This observation confirms the presence of the amino functional groups in pentane-1,5-diamine.
Step 2
Mass spectrum
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Answer
The mass spectrum shows the molecular ion peak corresponding to the fragment CH2NH2+ with a molecular weight of 30 (12 + 10 + 141 = 30), confirming the molecular formula is consistent with pentane-1,5-diamine.
Step 3
Carbon-13 NMR spectrum
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The carbon-13 NMR spectrum reveals three distinct signals due to the five carbon atoms in the molecule. Carbon atoms 1 and 5 are in identical environments, leading to overlapping signals. Carbon atom 3 has a unique chemical environment. The observed peaks at 24 and 33 ppm correlate with the CH2–CH2 carbon atoms (for carbons 1, 2, and 4), and the signal at 42 ppm corresponds to the C–N bond from the amino groups.
Step 4
Proton NMR
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The proton NMR spectrum displays a triplet corresponding to 4 hydrogen atoms and a quintet of 4 hydrogen atoms due to neighboring carbon environments. The overlapping quintets indicate six hydrogens are from two different environments, resulting in a total integration of the expected 6 hydrogen signal.
