Crystal and molecular structures of 1H-2-substituted

benzimidazoles

Pilar Cabildoa, Rosa M. Claramunta, Fco. Javier Zuñigab* Ibon Alkortac and Jose Elgueroc

Supplementary material


Figure S1. Structures of trimers linked by N–H···N bonds of compounds 1 to 7. We have represented a chain of three benzimidazole units for the compounds discussed in this paper. Note that in phase a of compound 3 there are two configurations, in phase b there are four, but only two of them are significantly different. In compound 4 there are four different configurations but local symmetries reduce to two significantly different.


Solid-State NMR

Solid-state 13C (100.73 MHz) CPMAS NMR spectra have been obtained on a Bruker WB 400 spectrometer at 300(1) K using a 4 mm DVT probe head. Samples were carefully packed in a 4-mm diameter cylindrical zirconia rotor with Kel-F end-caps. Operating conditions involved 3.2 µs 90° 1H pulses and decoupling field strength of 78.1 kHz by TPPM sequence. 13C spectra were originally referenced to a glycine sample and then the chemical shifts were recalculated to the Me4Si [for the carbonyl atom d13C(glycine) = 176.1 ppm]; and 15N spectra to 15NH4Cl and then converted to nitromethane scale using the relationship: d15N(nitromethane) = d 15N(ammonium chloride) – 338.1 ppm. Typical acquisition parameters for 13C CPMAS were: spectral width, 40 kHz; recycle delay, 5 s; acquisition time, 30 ms; contact time, 2 ms; and spin rate, 12 kHz. In order to distinguish protonated and non-protonated carbon atoms, the NQS (Non-Quaternary Suppression) experiment by conventional cross-polarization was recorded; before the acquisition the decoupler is switched off for a very short time of 25 ms. And for 15N CPMAS were: spectral width, 40 kHz; recycle delay, 5 s; acquisition time, 35 ms; contact time, 4 ms; and spin rate, 6 kHz (Murphy, 1985, Alemany et al., 1983).

Figures S1, S2 and S3 report the spectra of the more interesting compounds, 3, 4 and 7.The results are reported in Tables T1 and T2. An X-ray powder diffraction pattern from a sample of compound 3 used in the NMR experiment confirms that it correspond to the form (3a) (see Figure S-4).

Figure S2. 13C and 15N CPMAS NMR spectrum of 3 (the scale of 15N is referred to ammonium chloride (–338.1 ppm from nitromethane).

Figure S3. 13C and 15N CPMAS NMR spectrum of 4 (the scale of 15N is referred to ammonium chloride (–338.1 ppm from nitromethane).

Figure S4. 13C (left) and 15N (right) CPMAS NMR spectra of 7 (the scale of 15N is referred to ammonium chloride (–338.1 ppm from nitromethane).

Figure S5. X-ray powder diffraction pattern from a sample of compound 3 used in the NMR experiment confirms that it correspond to the form (3a).

Table T1. 13C CPMAS NMR chemical shifts (δ in ppm) of 1H-benzimidazoles. Split signal values are given in two lines.

Compound / C2 / C3a / C4 / C5 / C6 / C7 / C7a / R
1H-Benzimidazole (1)a / 143.1 / 143.1 / 118.3
120.4 / 123.0 / 123.8 / 112.9 / 136.4 / ----
2-Methyl-1H-benzimidazole (2) / 153.6 / 142.9 / 117.4 / 121.7 / 121.7 / 111.6 / 134.7 / 12.6
2-Ethyl-1H-benzimidazole (3)b / 156.4 / 141.2
142.9 / 116.7
118.0 / 120.0
122.4 / 120.0
122.4 / 110.8
112.4 / 135.5 / 22.3; 11.2; 7.0
2-Propyl-1H-benzimidazole (4) / 157.8 / 141.8 / 120.5 / 122.5 / 122.5 / 112.6 / 135.3 / 31.0; 21.8; 13.1
2-Butyl-1H-benzimidazole (5) / 156.0 / 142.8 / 118.6 / 120.7 / 122.8 / 112.2 / 135.8 / 29.8; 23.1; 12.4
2-Benzyl-1H-benzimidazole (6) / 156.6 / 143.0 / 119.4 / 120.5 / 122.8 / 113.4 / 135.0 / 36.0; 136.2 (ipso); ~127 (br, ortho, meta); 124.3 (para)
2-Phenyl-1H-benzimidazole (7) / 152.2 / 142.6 / 116.2
117.7 / 122.9 / 122.9 / 110.8
112.4 / 135.3 / 126.5 (ipso); 129.3 (meta and para)

a From references (it corresponds to polymorph α) (Faure et al., 1983, Claramunt et al., 2001).

b Correspond to polymorphs 3a.

Table T2. 15N CPMAS NMR chemical shifts (δ in ppm) of 1H-benzimidazoles referenced to external CH3NO2

Compound / N1 / N3
Benzimidazole (1)a / –221.8 / –143.9
2-Methylbenzimidazole (2) / –219.5; –224.2 / –146.9
2-Ethylbenzimidazole (3)b / –220.4; –224.6 / –147.7; –151.7
2-Propylbenzimidazole (4) / –218.5; –222.7 / –147.3
2-Butylbenzimidazole (5) / –223.2 / –147.7
2-Benzylbenzimidazole (6) / –221.8 / –147.2
2-Phenylbenzimidazole (7) / –225.7; –230.0 / –154.8

a The 15N CPMAS NMR spectrum of 1 was recorded but the 15N NMR signals were not observed (Claramunt et al., 2001). Data were reported but the assignment of both nitrogen atoms was reversed (Solum et al., 1997).

b Correspond to polymorphs 3a.

References

Claramunt, R. M.; López, C.; Sanz, D.; Alkorta I.; and Elguero, J.; (2001) Heterocycles, 55, 2109–2121.

Faure, R.; Vincent, E.-J.; Elguero, J. (1983). Heterocycles, 20, 1713–1716.

Solum, M. S.; Altmann, K. L.; Strohmeier, M.; Berges, D. A.; Zhang, Y.; Facelli, J. C.; Pugmire, R. J.; Grant, D. M. (1997). J. Am. Chem. Soc.; 119, 9804–9809.

Alemany, L. B.; Grant, D. M.; Alger, T. D.; Pugmire, R. J. (1983). J. Am. Chem. Soc. 105, 6697–6704.

Murphy, P. D. (1983). J. Magn. Reson.; 52, 343–345, ibid. (1985), 62, 303–308.

DSC

Experiments to determine the melting points were performed by DSC with a SEIKO DSC 220 C connected to a SSC5200H model disk station; thermograms (sample weight 0.003-0.005 g) were recorded with a scan rate of 5.0 K/min. Melting temperatures found are 446.2 K and 431.6 K for compounds 3 and 4 respectively. DSC experiment on compound 3 performed at low temperature with a Q2000 (TA Instruments).

Figure S6. DSC plots of 2-ethyl-1H-benzimidazole (3). Cooling and heating cycles are indicated with the arrow.

Figure S7. Wires model of the molecule type I in the form (3a) showing the disordered positions. Planes of benzimidazoles form a dihedral angle of 8.1º.

Figure S8. Torsion angles of the C-C bond between the benzimidazole ring and the propyl group (the other torsion, involving the methyl group, C1-C8-C9-C10, C11-C18-C19-C20, C21-C28-C29-C30 and C31-C38-C39-C40, has values 172.9º, -178.0º, -170.0º and 172.6º respectively); molecules 1 and 4 with an average faver = +44.9(6)º and molecules 2 and 3 with faver = –45.2(2)º.

Figure S9. Representation of the torsion angle D (C2-N1-N3'-C2'). For compounds that have several independent molecules we have used average values.