Crystal structures of racemic and enanti­opure synephrine correlated with physicochemical properties from IR spectroscopy and thermal analysis

Fujii, I.

doi:10.1107/S2053229618014419

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Crystal structures of racemic and enantiopure synephrine correlated with physicochemical properties from IR spectroscopy and thermal analysis

I. Fujii

The proto-alkaloid synephrine {SYN; systematic name: 4-[1-hydroxy-2-(methylamino)ethyl]phenol}, C₉H₁₃NO₂, is found to crystallize as a neutral molecule in the racemate and as a zwitterion in the pure enantiomer, in which the phenolic H atom has been transferred to the amino group. In the racemate crystal, an enantiomeric pair on an inversion centre is weakly linked by alcoholic O—H and N—H groups into an R₂²(10) ring. The trigonal pyramidal amino group is also linked to the phenolic and alcoholic groups to form a C(6) chain. In the enantiopure crystal, the deprotonated phenolic O atom is involved in trifurcated hydrogen bonding to two quaternary ammonium groups and an alcoholic O—H group to form a fused R₂⁴(11) ring and a C(7) chain. From the results of the crystal structure analysis, thermal analyses and DFT calculations validated from FT–IR spectra, a different tautomer was found in the racemic molecule (RS-SYN) versus the enantiopure molecule (R-SYN).

Keywords: proto-alkaloid; zwitterion; synephrine; crystal structure; HOMO–LUMO energy gap; IR spectra; thermal analysis.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S2053229618014419/qf3019sup1.cif Contains datablocks global, RS-SYN, R-SYN
	Structure factor file (CIF format) https://doi.org/10.1107/S2053229618014419/qf3019RS-SYNsup2.hkl Contains datablock RS-SYN
	Structure factor file (CIF format) https://doi.org/10.1107/S2053229618014419/qf3019R-SYNsup3.hkl Contains datablock R-SYN
	Chemical Markup Language (CML) file https://doi.org/10.1107/S2053229618014419/qf3019R-SYNsup4.cml Supplementary material

CCDC references: 1872931; 1872930

Computing details top

For both structures, data collection: CrystalClear-SM Expert (Rigaku, 2015); cell refinement: CrystalClear-SM Expert (Rigaku, 2015); data reduction: SORTAV (Blessing, 1995) and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL2017 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: PLATON (Spek, 2009), WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).

4-[1-Hydroxy-2-(methylamino)ethyl]phenol (RS-SYN) top

Crystal data top

C₉H₁₃NO₂	F(000) = 360
M_r = 167.2	D_x = 1.287 Mg m⁻³
Monoclinic, P2₁/n	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: -P 2yn	Cell parameters from 653 reflections
a = 8.768 (3) Å	θ = 25.5–68°
b = 11.935 (4) Å	µ = 0.74 mm⁻¹
c = 9.001 (3) Å	T = 100 K
β = 113.623 (9)°	Prism, colorless
V = 863.0 (5) Å³	0.4 × 0.3 × 0.2 mm
Z = 4

Data collection top

Rigaku XtaLAB P200 diffractometer	1546 independent reflections
Radiation source: sealed x-ray tube	1107 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.072
Detector resolution: 5.81 pixels mm^-1	θ_max = 68.3°, θ_min = 7.0°
phi or ω oscillation scans	h = −10→10
Absorption correction: multi-scan (REQAB; Rigaku, 1998)	k = −14→14
T_min = 0.74, T_max = 0.86	l = −10→10
4832 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.049	Hydrogen site location: mixed
wR(F²) = 0.131	H atoms treated by a mixture of independent and constrained refinement
S = 0.95	w = 1/[σ²(F_o²) + (0.0795P)²] where P = (F_o² + 2F_c²)/3
1546 reflections	(Δ/σ)_max < 0.001
119 parameters	Δρ_max = 0.41 e Å⁻³
0 restraints	Δρ_min = −0.2 e Å⁻³
0 constraints

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O1	0.19178 (18)	0.73325 (13)	1.16284 (17)	0.0282 (4)
H1O	0.203997	0.673758	1.216264	0.042*
O2	0.48132 (18)	0.59805 (13)	0.64037 (16)	0.0258 (4)
N1	0.2175 (2)	0.55872 (16)	0.34169 (18)	0.0255 (4)
C1	0.2981 (2)	0.68056 (17)	0.7561 (2)	0.0220 (5)
C2	0.2115 (3)	0.77427 (18)	0.7695 (2)	0.0256 (5)
H2	0.176651	0.828257	0.68487	0.031*
C3	0.1745 (3)	0.79101 (18)	0.9042 (2)	0.0267 (5)
H3	0.113278	0.855362	0.909881	0.032*
C4	0.2268 (2)	0.71378 (18)	1.0312 (2)	0.0232 (5)
C5	0.3152 (2)	0.61982 (18)	1.0196 (2)	0.0246 (5)
H5	0.352336	0.566588	1.105246	0.03*
C6	0.3494 (2)	0.60360 (18)	0.8833 (2)	0.0249 (5)
H6	0.408986	0.538688	0.876586	0.03*
C7	0.3288 (2)	0.65820 (17)	0.6044 (2)	0.0230 (5)
H7	0.333437	0.73109	0.551555	0.028*
C8	0.1883 (2)	0.58744 (19)	0.4872 (2)	0.0256 (5)
H8A	0.178222	0.517709	0.542175	0.031*
H8B	0.082222	0.629101	0.45466	0.031*
C9	0.0896 (3)	0.4819 (2)	0.2361 (2)	0.0327 (5)
H9A	0.083461	0.416044	0.2986	0.049*
H9B	0.118195	0.458184	0.146243	0.049*
H9C	−0.018466	0.520003	0.192977	0.049*
H2O	0.562 (4)	0.645 (3)	0.662 (4)	0.054 (9)*
H1N	0.314 (3)	0.523 (2)	0.377 (3)	0.028 (6)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0360 (8)	0.0323 (9)	0.0218 (7)	0.0076 (7)	0.0172 (6)	0.0022 (6)
O2	0.0247 (8)	0.0304 (9)	0.0240 (7)	0.0004 (7)	0.0113 (6)	−0.0013 (6)
N1	0.0248 (9)	0.0349 (11)	0.0159 (8)	0.0027 (8)	0.0072 (7)	−0.0012 (7)
C1	0.0185 (9)	0.0289 (12)	0.0175 (9)	−0.0012 (8)	0.0062 (7)	−0.0024 (8)
C2	0.0284 (11)	0.0274 (12)	0.0219 (10)	0.0037 (9)	0.0109 (8)	0.0036 (8)
C3	0.0300 (11)	0.0262 (11)	0.0260 (10)	0.0048 (9)	0.0132 (9)	0.0000 (8)
C4	0.0218 (10)	0.0313 (12)	0.0179 (10)	−0.0002 (9)	0.0094 (8)	−0.0046 (8)
C5	0.0242 (10)	0.0307 (12)	0.0188 (9)	0.0047 (9)	0.0084 (8)	0.0027 (8)
C6	0.0256 (10)	0.0280 (11)	0.0210 (10)	0.0045 (8)	0.0091 (8)	−0.0016 (8)
C7	0.0252 (10)	0.0257 (11)	0.0187 (9)	0.0030 (8)	0.0093 (8)	0.0025 (8)
C8	0.0267 (10)	0.0338 (12)	0.0177 (9)	0.0005 (9)	0.0103 (8)	0.0010 (8)
C9	0.0346 (11)	0.0421 (14)	0.0197 (9)	−0.0051 (10)	0.0090 (8)	−0.0021 (9)

Geometric parameters (Å, º) top

O1—C4	1.358 (2)	C3—H3	0.95
O1—H1O	0.84	C4—C5	1.391 (3)
O2—C7	1.436 (2)	C5—C6	1.388 (3)
O2—H2O	0.86 (4)	C5—H5	0.95
N1—C9	1.465 (3)	C6—H6	0.95
N1—C8	1.472 (2)	C7—C8	1.517 (3)
N1—H1N	0.88 (3)	C7—H7	1
C1—C2	1.384 (3)	C8—H8A	0.99
C1—C6	1.394 (3)	C8—H8B	0.99
C1—C7	1.518 (3)	C9—H9A	0.98
C2—C3	1.389 (3)	C9—H9B	0.98
C2—H2	0.95	C9—H9C	0.98
C3—C4	1.395 (3)

C4—O1—H1O	109.5	C5—C6—H6	119.3
C7—O2—H2O	110 (2)	C1—C6—H6	119.3
C8—N1—C9	111.24 (16)	O2—C7—C8	107.58 (16)
C9—N1—H1N	107.8 (16)	O2—C7—C1	111.69 (15)
C8—N1—H1N	105.9 (15)	C8—C7—C1	109.64 (16)
C2—C1—C6	117.94 (17)	O2—C7—H7	109.3
C2—C1—C7	121.44 (17)	C8—C7—H7	109.3
C6—C1—C7	120.54 (18)	C1—C7—H7	109.3
C1—C2—C3	121.35 (19)	N1—C8—C7	111.48 (16)
C1—C2—H2	119.3	N1—C8—H8A	109.3
C3—C2—H2	119.3	C7—C8—H8A	109.3
C2—C3—C4	120.31 (19)	N1—C8—H8B	109.3
C2—C3—H3	119.8	C7—C8—H8B	109.3
C4—C3—H3	119.8	H8A—C8—H8B	108
O1—C4—C5	122.06 (18)	N1—C9—H9A	109.5
O1—C4—C3	119.13 (18)	N1—C9—H9B	109.5
C5—C4—C3	118.81 (18)	H9A—C9—H9B	109.5
C6—C5—C4	120.17 (18)	N1—C9—H9C	109.5
C6—C5—H5	119.9	H9A—C9—H9C	109.5
C4—C5—H5	119.9	H9B—C9—H9C	109.5
C5—C6—C1	121.41 (19)

C6—C1—C2—C3	−0.8 (3)	C7—C1—C6—C5	−176.76 (18)
C7—C1—C2—C3	175.90 (19)	C2—C1—C7—O2	149.85 (18)
C1—C2—C3—C4	1.1 (3)	O2—C7—C1—C6	−33.5 (3)
C2—C3—C4—O1	178.73 (18)	C2—C1—C7—C8	−91.0 (2)
C2—C3—C4—C5	−0.4 (3)	C6—C1—C7—C8	85.6 (2)
O1—C4—C5—C6	−179.51 (17)	C9—N1—C8—C7	174.72 (17)
C3—C4—C5—C6	−0.4 (3)	O2—C7—C8—N1	−55.4 (2)
C4—C5—C6—C1	0.6 (3)	C1—C7—C8—N1	−177.02 (16)
C2—C1—C6—C5	0.0 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···N1ⁱ	0.84	1.75	2.587 (2)	173
O2—H2O···O1ⁱⁱ	0.86 (4)	1.84 (4)	2.683 (2)	164 (3)
N1—H1N···O2ⁱⁱⁱ	0.88 (3)	2.36 (3)	3.188 (2)	156 (2)

Symmetry codes: (i) x, y, z+1; (ii) x+1/2, −y+3/2, z−1/2; (iii) −x+1, −y+1, −z+1.

4-[1-Hydroxy-2-(methylamino)ethyl]phenol (R-SYN) top

Crystal data top

C₉H₁₃NO₂	F(000) = 360
M_r = 167.2	D_x = 1.265 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: P 2ac 2ab	Cell parameters from 1029 reflections
a = 6.5581 (15) Å	θ = 25.7–68.2°
b = 7.8144 (18) Å	µ = 0.73 mm⁻¹
c = 17.137 (5) Å	T = 100 K
V = 878.2 (4) Å³	Plate, colorless
Z = 4	0.4 × 0.4 × 0.2 mm

Data collection top

Rigaku XtaLAB P200 diffractometer	1586 independent reflections
Radiation source: sealed x-ray tube	1504 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.047
Detector resolution: 5.81 pixels mm^-1	θ_max = 68.2°, θ_min = 7.2°
phi or ω oscillation scans	h = −7→7
Absorption correction: multi-scan (REQAB; Rigaku, 1998)	k = −9→9
T_min = 0.74, T_max = 0.88	l = −20→18
7138 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.028	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.098	w = 1/[σ²(F_o²) + (0.0659P)²] where P = (F_o² + 2F_c²)/3
S = 1.17	(Δ/σ)_max < 0.001
1586 reflections	Δρ_max = 0.24 e Å⁻³
122 parameters	Δρ_min = −0.20 e Å⁻³
0 restraints	Absolute structure: Flack x determined using 590 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
0 constraints	Absolute structure parameter: −0.06 (10)
Primary atom site location: structure-invariant direct methods

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.3094 (3)	0.4999 (2)	0.20752 (10)	0.0194 (4)
C2	0.3508 (3)	0.4273 (3)	0.28024 (12)	0.0228 (4)
H2	0.433068	0.327445	0.28316	0.027*
C3	0.2739 (3)	0.4983 (2)	0.34833 (11)	0.0222 (4)
H3	0.302665	0.445235	0.396965	0.027*
C4	0.1541 (3)	0.6474 (2)	0.34669 (11)	0.0198 (4)
C5	0.1139 (3)	0.7205 (3)	0.27349 (12)	0.0227 (5)
H5	0.034331	0.821861	0.27039	0.027*
C6	0.1885 (3)	0.6470 (3)	0.20571 (11)	0.0220 (4)
H6	0.156654	0.697832	0.156847	0.026*
C7	0.3849 (3)	0.4194 (3)	0.13296 (11)	0.0212 (4)
H7	0.428814	0.299104	0.143749	0.025*
C8	0.5630 (3)	0.5188 (2)	0.09937 (11)	0.0210 (5)
H8A	0.518637	0.636498	0.086467	0.025*
H8B	0.673172	0.526414	0.138721	0.025*
C9	0.7764 (3)	0.5442 (3)	−0.01937 (12)	0.0289 (5)
H9A	0.900282	0.570073	0.010358	0.043*
H9B	0.704806	0.650957	−0.031647	0.043*
H9C	0.813238	0.485645	−0.06793	0.043*
N1	0.6424 (2)	0.4329 (2)	0.02740 (10)	0.0206 (4)
O1	0.0845 (2)	0.71864 (18)	0.41231 (7)	0.0229 (4)
O2	0.2353 (2)	0.41891 (19)	0.07252 (8)	0.0276 (4)
H1NA	0.536 (4)	0.396 (3)	−0.0024 (15)	0.031 (6)*
H1NB	0.736 (5)	0.344 (4)	0.0406 (16)	0.050 (8)*
H2O	0.127 (6)	0.348 (4)	0.0888 (18)	0.062 (10)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0150 (9)	0.0248 (9)	0.0186 (9)	−0.0034 (7)	0.0013 (7)	−0.0005 (7)
C2	0.0177 (9)	0.0271 (9)	0.0235 (10)	0.0028 (8)	−0.0013 (7)	0.0010 (8)
C3	0.0194 (9)	0.0307 (9)	0.0165 (9)	0.0019 (8)	−0.0029 (8)	0.0040 (7)
C4	0.0133 (9)	0.0285 (9)	0.0177 (9)	−0.0028 (8)	0.0000 (7)	−0.0010 (8)
C5	0.0198 (10)	0.0253 (9)	0.0231 (10)	0.0040 (8)	0.0010 (8)	0.0025 (8)
C6	0.0208 (10)	0.0292 (9)	0.0159 (9)	0.0004 (8)	0.0000 (8)	0.0047 (7)
C7	0.0190 (9)	0.0269 (9)	0.0178 (10)	−0.0024 (8)	0.0003 (7)	−0.0014 (8)
C8	0.0185 (10)	0.0253 (9)	0.0191 (10)	−0.0013 (8)	0.0015 (8)	−0.0032 (7)
C9	0.0260 (10)	0.0358 (10)	0.0250 (10)	−0.0039 (9)	0.0067 (9)	0.0051 (9)
N1	0.0171 (8)	0.0279 (8)	0.0167 (8)	−0.0007 (7)	0.0017 (6)	0.0000 (7)
O1	0.0197 (6)	0.0316 (7)	0.0174 (7)	0.0019 (6)	0.0025 (6)	−0.0009 (5)
O2	0.0213 (7)	0.0431 (9)	0.0184 (7)	−0.0080 (7)	−0.0004 (5)	−0.0027 (6)

Geometric parameters (Å, º) top

C1—C2	1.396 (3)	C7—C8	1.516 (3)
C1—C6	1.397 (3)	C7—H7	1
C1—C7	1.508 (3)	N1—C8	1.497 (2)
C2—C3	1.387 (3)	C8—H8A	0.99
C2—H2	0.95	C8—H8B	0.99
C3—C4	1.405 (3)	N1—C9	1.473 (3)
C3—H3	0.95	C9—H9A	0.98
O1—C4	1.335 (2)	C9—H9B	0.98
C4—C5	1.404 (3)	C9—H9C	0.98
C5—C6	1.385 (3)	N1—H1NA	0.91 (3)
C5—H5	0.95	N1—H1NB	0.95 (3)
C6—H6	0.95	O2—H2O	0.94 (4)
O2—C7	1.427 (2)

C2—C1—C6	117.69 (16)	C1—C7—H7	109.3
C2—C1—C7	121.54 (17)	C8—C7—H7	109.3
C6—C1—C7	120.73 (15)	N1—C8—C7	110.55 (16)
C3—C2—C1	121.18 (18)	N1—C8—H8A	109.5
C3—C2—H2	119.4	C7—C8—H8A	109.5
C1—C2—H2	119.4	N1—C8—H8B	109.5
C2—C3—C4	121.21 (16)	C7—C8—H8B	109.5
C2—C3—H3	119.4	H8A—C8—H8B	108.1
C4—C3—H3	119.4	N1—C9—H9A	109.5
O1—C4—C5	121.22 (17)	N1—C9—H9B	109.5
O1—C4—C3	121.35 (15)	H9A—C9—H9B	109.5
C5—C4—C3	117.42 (16)	N1—C9—H9C	109.5
C6—C5—C4	120.95 (18)	H9A—C9—H9C	109.5
C6—C5—H5	119.5	H9B—C9—H9C	109.5
C4—C5—H5	119.5	C8—N1—C9	113.03 (16)
C5—C6—C1	121.54 (16)	C9—N1—H1NA	109.8 (15)
C5—C6—H6	119.2	C8—N1—H1NA	109.7 (16)
C1—C6—H6	119.2	C9—N1—H1NB	100.1 (18)
O2—C7—C1	112.97 (15)	C8—N1—H1NB	110.7 (16)
O2—C7—C8	104.80 (15)	H1NA—N1—H1NB	113 (2)
C1—C7—C8	111.16 (16)	C7—O2—H2O	107.8 (19)
O2—C7—H7	109.3

C6—C1—C2—C3	0.3 (3)	C7—C1—C6—C5	178.52 (18)
C7—C1—C2—C3	−177.39 (17)	O2—C7—C1—C2	137.31 (18)
C1—C2—C3—C4	−1.0 (3)	O2—C7—C1—C6	−40.3 (2)
C2—C3—C4—O1	−178.18 (18)	C2—C1—C7—C8	−105.2 (2)
C2—C3—C4—C5	0.6 (3)	C6—C1—C7—C8	77.2 (2)
O1—C4—C5—C6	179.28 (18)	O2—C7—C8—N1	−60.22 (19)
C3—C4—C5—C6	0.5 (3)	C1—C7—C8—N1	177.43 (15)
C4—C5—C6—C1	−1.3 (3)	C7—C8—N1—C9	164.65 (16)
C2—C1—C6—C5	0.9 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1NA···O1ⁱ	0.91 (3)	1.89 (3)	2.740 (2)	155 (2)
N1—H1NB···O1ⁱⁱ	0.95 (3)	1.73 (3)	2.661 (2)	164 (3)
O2—H2O···O1ⁱⁱⁱ	0.94 (4)	1.72 (4)	2.630 (2)	162 (3)

Symmetry codes: (i) −x+1/2, −y+1, z−1/2; (ii) −x+1, y−1/2, −z+1/2; (iii) −x, y−1/2, −z+1/2.

Selected comparison of the calculated harmonic frequencies and experimental wavenumbers (FT–IR) of RS-SYN. top

FT–IR (cm^-1)	Peaks profile*	Calc. freq. (cm^-1)	Calc. int.	PEDs (%)	Mode sssign.**
3050–3670	BVS	3677	37.4	νO1H(100)	ν(O—H)
		3657	8.5	νO2H(100)	ν(O—H)
3287	VS	3533	4.3	νN1H(99)	ν(N—H)
2983	M	3072	41.8	νC8H(91)	ν(C—H)
2959	M	3006	56.7	νC7H(93)	ν(C—H)
2877	M	2936	132.0	νC9H3(90)	ν(C—H)
1611	M	1736	67.5	νC2C3(28)+νC5C6(11)	ν(C═C)
		1690	5.2	νC1C6(27)-νC4C5(19)	ν(C═C)
1509	S	1612	88.3	νC4C5(13)-νC4O1(12)	ν(C—O)
1465	M	1509	16.9	δC9N1H(42)-δC7C8N1H(11)	δ(N—H)
1435	M	1496	22.1	δC9N1H(24)-δsHC9H(29)	δ(N—H)
1336	M	1378	93.0	νC4O1(40)	ν(C—O)
1309	M	1345	30.0	νC1C7(15)+δC7O2H(13)	δ(O—H)
1266	S	1267	10.6	νC1C7(13)+δN1C8H(10)	δ(C—H)
		1260	2.4	νC1C7(16)-δC7O2H(13)	δ(O—H)
1205	M	1212	165.1	δC4O1H(41)-δC6C5H(10)	δ(O—H)
1097	S	1100	63.5	νC7O2(32)-δN1C8H(12)	ν(C—O)
1054	S	1070	7.9	νC7C8(21)-νC9N1(11)+δC7O2H(2)	ν(C-N), δ(O—H)
930	BM	947	16.6	-νC7C8(19)-νC7O2(25)	ν(C—O)
884	M	873	40.3	δC3H(45)+δC2H(31)	δ(C—H)
835	S	854	30.0	δC6H(21)+δC5H(62)	δ(C—H)'
780	M	767	94.7	-δC9N1H(12)+γC7C8N1H(47)	δ(N—H)
637	M	598	32.6	δC4C5C6(22)	δ(C—C)
575	M	564	32.9	δC6C7C8(11)+δC8C7O2(12)	δ(C—O)
558	M	540	3.4	γO1C4C5C6(14)	γ(C—O)

Notes: (*) B = broad, V = very, W = weak, M = medium and S = strong peaks. (**) ν = stretching, δ = bending and γ = rocking vibrations.

Selected comparison of the calculated harmonic frequencies and experimental wavenumbers (FT–IR) of R-SYN. top

FT–IR (cm^-1)	Peaks profile*	Calc. freq. (cm^-1)	Calc. int.	PEDs (%)	Mode assign.**
3300–3610	BM	3712	85.2	νO2H(100)	ν(O—H)
3041	W	3204	18.1	νC5H(95)	ν(C—H)
3013	W	3200	28.1	νC3H(95)	ν(C—H)
2930–3100	BM	3462	48.4	νN1H(94)	ν(N—H)
2938	VW	3112	19.4	νC2H(33)+νC6H(64)	ν(C—H)
2871	VW	3110	61.5	νC2H(65)-νC6H(34)	ν(C—H)
2590-2880	BM	3345	68.5	νN1H(93)	ν(N—H)
2763	W	3095	10.0	-νC9H(30)-νC9H(25)-νC9H(44)	ν(C—H)
2723	W	2932	73.5	νC7H(90)	ν(C—H)
1605	BM	1703	38.8	δsN1H₂(87)	δs(N—H)
1558	M	1653	94.9	-νC2C3(10)+νC1C6(31)	ν(C═C)
1542	M	1644	157.4	-νC2C3(24)+νC4C5(29)	ν(C═C)
1499	S	1544	18.7	νC3C4(13)	ν(C═C)
1488	S	1534	20.0	δC9H₂(38)	δas(C—H)
		1527	16.5	δC9H₂(43)	δs(C—H)
1466	S	1503	20.9	δC8H₂(39)+δC9H₂(18)	δs(C—H)
		1499	20.6	-νC2C3(32)+νC5C6(32)	δ(C═C)
1426	M	1448	35.6	δO2C7H(15)	δ(C—H)
		1433	166.6	δHC9N1H1(18)-δHC9N1H2(38)	δs(N—H)
1341	M	1360	69.3	δC7O2H(16)-δC9N1H(10)	δ(O—H), δ(N—H)
1249	BVS	1274	185.5	-νC5C6(12)+νC4O1(54)	ν(C═O)
		1272	49.7	-δC7O2H(25)+δO2C7H(21)	δ(O—H)
1209	M	1214	28.4	-νC6C1(17)+δO2C7H(10)	δ(C—H)
1159	S	1187	14.6	δO2C7H(10)	δ(C—H)
1146	M	1177	118.2	δC2H(17)+δC3H(17)	δs(C—H)
1077	M	1156	9.1	δO2C7H(10)+δC9H₃(10)	δ(C—H)
1058	M	1115	8.4	δC4C3H(15)+δC6C5H(20)	δ(C—H)
1032	M	1073	18.7	νC9N1(69)	ν(C—N)
971	BM	1059	116.2	-νC7C8(18)+νC7O2(39)	ν(C—O)
842	S	902	125.3	νC8N1(55)	ν(C—N)
802	M	849	44.7	γC2H(20)	γ(C—H)
589	M	574	16.4	δC3C4C5(22)	δ(C—C)
559	M	541	32.6	δC8C7O2(21)	δ(C—O)
469	M	430	10.1	δC1C7C8(21)-δC8N1C9(13)	δ(C—N)

Notes: (*) B = broad, V = very, W = weak, M = medium and S = strong peaks. (**) ν = stretching, δ = bending and γ = rocking vibrations.

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Crystal structures of racemic and enanti­opure synephrine correlated with physicochemical properties from IR spectroscopy and thermal analysis

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Crystal structures of racemic and enantiopure synephrine correlated with physicochemical properties from IR spectroscopy and thermal analysis