Systematic discovery about NIR spectral assignment from chemical structural property to natural chemical compounds

Spectra-structure interrelationship is still the weakness of NIR spectral assignment. In this paper, a comprehensive investigation from chemical structural property to natural chemical compounds was carried out for NIR spectral assignment. Surprisingly, we discovered that NIR absorption frequency of the skeleton structure with sp2 hybridization is higher than one with sp3 hybridization. Specifically, substituent was another vital factor to be explored, the first theory discovery demonstrated that the absorption intensity of methyl substituted benzene at 2330 nm has a linear relationship with the number of substituted methyl C-H. The greater the number of electrons given to the substituents, the larger the displacement distance of absorption bands is. In addition, the steric hindrance caused by the substituent could regularly reduce the intensity of NIR absorption bands. Furthermore, the characteristic bands and group attribution of 29 natural chemical compounds from 4 types have been systematic assigned. These meaningful discoveries provide guidance for NIR spectral assignment from chemical structural property to natural chemical compounds.


Figure S2
The partially enlarged DS of methyl substituted benzenes and benzene. At 1138 nm, 1670 nm, and 2130 nm, the order of absorption peak intensity from large to small was ethylbenzene > toluene > xylene > mesitylene.

Figure S3
The NIR DS between methyl substituted benzenes and toluene. From this figure, the differences at 2330 nm caused by methyl could be seen and the order of absorption peak intensity from large to small was ethylbenzene > toluene > xylene > mesitylene.

Figure S4
The partially enlarged view of the NIRS DS between xylenes and benzene. the absorption intensities caused by benzene ring skeleton of xylenes at 1138 nm, 1670 nm and 2130 nm were negatively correlated with their symmetry, with the order as ortho-xylene < meta-xylene < para-xylene.

Figure S5
The partially enlarged view of NIRS DS between xylenes and benzene and NIRS DS between xylenes and toluene.

Figure S6
The two subtraction DS of xylenes. There were some certain absorptive distinctions of ortho-xylene, meta-xylene, and para-xylene at 1700 nm and combination mode at 2100-2500 nm.

Figure S7
The NIR 2nd spectra of benzene, phenol, benzyl alcohol, benzaldehyde. In this figure, phenol and benzyl alcohol both had absorption at 970 nm and 1410 nm, while benzaldehyde did not.

Figure S8
The NIR DS of phenol, benzyl alcohol, benzaldehyde, and benzene, in which phenol and benzyl alcohol had strong characteristic absorption at 1410 nm and there were obvious distinctions at the range of 2050-2350 nm.

Figure S10
The partial enlargement of the 2nd spectra of phenylalanines.

Figure S12
The partial enlargement of the 2nd spectra of lignins, including Schisandra B, Schisandra A, Schisandrin A, Schizandrol, and Ampicin.

Figure S15
The synchronous 2D-COS of magnolols with different sample concentration intervals. There are 12 same autocorrelation peaks caused by this 3 kinds of sample concentration intervals at 1339 nm, 1444 nm, 1631 nm, 1690 nm,

Table S1
The sample preparation for 2D-COS.

Table S2
The characteristic bands of several kinds of compounds assigned by the second derivative and 2D-COS, respectively.

Figure S1
The NIR raw spectrum of benzene and cyclohexane. There are obvious differences between the benzene and cyclohexane at 890 nm, 1210 nm, 1400 nm, and 1760 nm.

Figure S2
The partially enlarged DS of methyl substituted benzenes and benzene. At 1138 nm, 1670 nm, and 2130 nm, the order of absorption peak intensity from large to small was ethylbenzene > toluene > xylene > mesitylene.

Figure S3
The NIR DS between methyl substituted benzenes and toluene. From this figure, the differences at 2330 nm caused by methyl could be seen and the order of absorption peak intensity from large to small was ethylbenzene > toluene > xylene > mesitylene.

Figure S4
The partially enlarged view of the NIRS DS between xylenes and benzene. the absorption intensities caused by benzene ring skeleton of xylenes at 1138 nm, 1670 nm and 2130 nm were negatively correlated with their symmetry, with the order as ortho-xylene < meta-xylene < para-xylene.

Figure S5
The partially enlarged view of NIRS DS between xylenes and benzene and NIRS DS between xylenes and toluene.

Figure S6
The two subtraction DS of xylenes. There were some certain absorptive distinctions of ortho-xylene, meta-xylene, and para-xylene at 1700 nm and combination mode at 2100-2500 nm.

Figure S7
The NIR 2nd spectra of benzene, phenol, benzyl alcohol, benzaldehyde. In this figure, phenol and benzyl alcohol both had absorption at 970 nm and 1410 nm, while benzaldehyde did not.

Figure S8
The NIR DS of phenol, benzyl alcohol, benzaldehyde, and benzene, in which phenol and benzyl alcohol had strong characteristic absorption at 1410 nm and there were obvious distinctions at the range of 2050-2350 nm.

Figure S10
The partial enlargement of the 2nd spectra of phenylalanines.

Figure S12
The partial enlargement of the 2nd spectra of lignins, including Schisandra B, Schisandra A, Schisandrin A, Schizandrol, and Ampicin.