DL-Phenyl­alaninium nitrate

In the title compound, C₉H₁₂NO₂⁺·NO₃⁻, the phenyl­alaninium residue adopts a folded conformation. It forms a strong O—H...O hydrogen bond with the nitrate anion and is also involved in a zigzag head-to-tail hydrogen-bonding sequence (Z1). In the crystal packing of the title compound, the aggregation of the hydro­phobic layer about the x = 0 plane (parallel to the ab plane) is sandwiched between hydro­philic double layers at x = −½ and x = ½.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.047
• wR factor = 0.141
• Data-to-parameter ratio = 12.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSMU_01  Alert C The ratio of given/expected absorption coefficient lies
          outside the range 0.99 <> 1.01
          Calculated value of mu =     0.117
          Value of mu given      =     0.120

ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR') is < 0.90
          Tmin and Tmax reported:      0.754     0.990
          Tmin' and Tmax expected:      0.961     0.988
          RR' =      0.783
          Please check that your absorption correction is appropriate.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 2 Alert Level C = Please check

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S1. Comment

Phenylalanine is an essential amino acids and also one of the aromatic amino acids. As part of our ongoing research programme studying hydrogen-bonding features and aggregation patterns of phenylalanine in the presence of various inorganic acids, a number of crystal structures, viz., L-phenylalanine L-phenylalaninium perchlorate (Srinivasan & Rajaram, 1997), bis(DL-phenylalaninium) sulfate monohydrate (Srinivasan et al., 2001a), L-phenylalanine nitric acid (2/1) (Srinivasan et al., 2001b), DL-phenylalaninium dihydrogen phosphate (Ravikumar et al., 2001) and L-phenylalanine L-phenylalaninium dihydrogen phosphate (Ravikumar et al., 2002) have been reported. In the present paper, the crystal structure of DL-phenylalaninium nitrate, (I), is described. The asymmetric unit contains one phenylalaninium residue and one nitrate anion (Fig. 1).

The bond distances and bond angles of phenylalaninium residue are within the expected ranges. The conformation angle ψ¹ (O1A—C1—C2—N1) corresponds to the cis form [−34.0 (5) °], the deviation of the amino nitrogen from the mean carboxyl plane being 0.80 (6) Å. This tendency for the C—N bond to twist is found in various amino acids (Lakshminarayanan et al., 1967). The angle between the carboxyl plane and phenyl ring plane is 51.2 (2)°. The branched side-chain conformation angle χ¹ (N1—C2—C3—C4) is equal to −174.7 (3)°, thus indicating the trans form. The other conformation angles χ²¹ and χ²² (C2—C3—-C4–C5 and C2—C3—C4—C9, respectively) are 81.2 (4) & −101.3 (5), and correspond to a folded conformation. The χ²¹ value lies within the expected range of 90±30° (Cotrait et al., 1984).

The nitrate anion plays a vital role in hydrogen bonding. However only two of the three oxygen atoms take part in hydrogen bonds. The N—O distances involving these two O atoms [1.254 (4) and 1.256 (4) Å] are slightly longer than the third N—O bond [1.234 (4) Å].

The phenylalaninium residue forms a strong O—H···O hydrogen bond with the nitrate anion. The amino nitrogen of the phenylalaninium residue forms an N—H···O hydrogen bond with oxygen atoms of the nitrate anion and the carboxyl oxygen atom (O1A). There is a zigzag (Z1) head-to-tail hydrogen-bonding sequence involving the amino nitrogen and carboxyl oxygen atoms (Table 2). The phenylalaninium cation in the title structure exhibits a hydrogen-bonding pattern with three two-centered hydrogen bonds [class I hydrogen-bonding pattern according to Jeffrey & Saenger (1991)]. The zigzag (Z1) head-to-tail sequence implies the hydrogen bonding between two 2₁ related amino acid molecules thus producing an infinite chain along the b axis of the crystal (Vijayan, 1988).

In the crystal packing of the title compound, the aggregation of the hydrophobic layer around the x = 0 plane (parallel to the yz plane) is sandwiched between hydrophilic double layers about x=-1/2 and x=1/2 (Fig. 2). Similar aggregation patterns are also observed in L-phenylalaninium formate (Görbitz & Etter, 1992), L-phenylalanine L-phenylalaninium perchlorate (Srinivasan & Rajaram, 1997), L-phenylalanine nitric acid (2/1) (Srinivasan et al., 2001b), DL-phenylalaninium dihydrogen phosphate (Ravikumar et al., 2001) and L-phenylalanine L-phenylalaninium dihydrogen phosphate (Ravikumar et al., 2002).

S2. Experimental

The title compound, (I), was crystallized from an aqueous solution of DL-phenylalanine and nitric acid by slow evaporation. The solution was prepared with 1 molar concentration of phenylalanine and 1 molar concentration of nitric acid with equal volumes (10 ml). The crystals were grown within one week.

S3. Refinement

All H atoms are placed in geometrically calculated positions and included in the refinement in a riding-model approximation, with U_iso equal to 1.2U_eq of the carrier atom (1.5U_eq for methyl and NH₃ H atoms).

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: CAD-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The phenylalaninium cation and the nitrate anion in the structure of the title compound, showing the atomic numbering scheme and 50% probability displacement ellipsoids (Johnson, 1976).
	Fig. 2. Packing diagram of the crystal of the title compound, viewed down the b axis.

DL-phenylalaninium nitrate

Crystal data

C9H12NO2^+·NO3^−	F(000) = 480
Mr = 228.21	Dx = 1.415 Mg m^−3 Dm = 1.413 Mg m^−3 Dm measured by flotation in a mixture of carbon tetrachloride and xylene
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 12.005 (7) Å	Cell parameters from 24 reflections
b = 5.758 (2) Å	θ = 8.1–13.9°
c = 16.250 (9) Å	µ = 0.12 mm^−1
β = 107.48 (6)°	T = 293 K
V = 1071.4 (9) Å^3	Needle, colorless
Z = 4	0.33 × 0.13 × 0.1 mm

Data collection

Enraf-Nonis sealed tube diffractometer	791 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.039
Graphite monochromator	θmax = 24.9°, θmin = 1.8°
ω–2θ scans	h = 0→14
Absorption correction: ψ-scan (North et al., 1968)	k = 0→6
Tmin = 0.754, Tmax = 0.990	l = −19→18
1968 measured reflections	3 standard reflections every 60 min
1874 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.047	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.141	H-atom parameters constrained
S = 0.96	w = 1/[σ^2(Fo^2) + (0.0614P)^2] where P = (Fo^2 + 2Fc^2)/3
1874 reflections	(Δ/σ)max < 0.001
145 parameters	Δρmax = 0.22 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3

Special details

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

treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N11	0.3794 (3)	−0.1150 (7)	0.4945 (2)	0.0361 (8)
O1	0.3883 (2)	−0.2873 (5)	0.45172 (18)	0.0483 (8)
O2	0.3997 (3)	−0.1306 (5)	0.57461 (16)	0.0474 (8)
O3	0.3507 (2)	0.0798 (5)	0.45976 (15)	0.0442 (8)
O1A	0.4162 (3)	−0.1177 (6)	0.25738 (16)	0.0526 (8)
O1B	0.3128 (2)	0.1680 (5)	0.29252 (16)	0.0523 (9)
H1	0.3330	0.1081	0.3405	0.078*
C1	0.3562 (3)	0.0495 (8)	0.2406 (2)	0.0339 (10)
C2	0.3201 (3)	0.1559 (7)	0.1500 (2)	0.0314 (10)
H2	0.3052	0.3222	0.1538	0.038*
N1	0.4185 (2)	0.1228 (6)	0.11343 (17)	0.0335 (8)
H1A	0.4822	0.1913	0.1474	0.050*
H1B	0.4002	0.1855	0.0610	0.050*
H1C	0.4321	−0.0283	0.1100	0.050*
C3	0.2121 (3)	0.0394 (8)	0.0906 (2)	0.0393 (11)
H3A	0.2006	0.0970	0.0326	0.047*
H3B	0.2274	−0.1259	0.0900	0.047*
C4	0.1004 (3)	0.0721 (7)	0.1124 (2)	0.0355 (10)
C5	0.0355 (4)	0.2708 (8)	0.0891 (3)	0.0489 (12)
H5	0.0639	0.3901	0.0624	0.059*
C6	−0.0718 (4)	0.2984 (9)	0.1043 (3)	0.0592 (14)
H6	−0.1151	0.4335	0.0873	0.071*
C7	−0.1131 (4)	0.1236 (11)	0.1449 (3)	0.0598 (14)
H7	−0.1846	0.1396	0.1555	0.072*
C8	−0.0491 (4)	−0.0722 (10)	0.1691 (3)	0.0569 (13)
H8	−0.0770	−0.1903	0.1967	0.068*
C9	0.0573 (4)	−0.0983 (8)	0.1533 (3)	0.0486 (11)
H9	0.1002	−0.2336	0.1707	0.058*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N11	0.0366 (19)	0.041 (2)	0.0353 (19)	−0.0078 (18)	0.0180 (15)	−0.0041 (19)
O1	0.0600 (19)	0.0457 (19)	0.0458 (17)	−0.0022 (15)	0.0261 (15)	−0.0145 (15)
O2	0.078 (2)	0.0453 (18)	0.0247 (14)	0.0001 (16)	0.0237 (13)	0.0014 (14)
O3	0.067 (2)	0.0395 (19)	0.0270 (14)	0.0020 (16)	0.0161 (14)	0.0062 (14)
O1A	0.072 (2)	0.058 (2)	0.0299 (15)	0.0275 (19)	0.0197 (14)	0.0103 (16)
O1B	0.072 (2)	0.065 (2)	0.0256 (14)	0.0208 (17)	0.0240 (14)	0.0062 (14)
C1	0.035 (2)	0.042 (3)	0.026 (2)	−0.002 (2)	0.0097 (18)	−0.004 (2)
C2	0.035 (2)	0.038 (3)	0.0221 (18)	0.0057 (19)	0.0115 (17)	0.0033 (18)
N1	0.0427 (19)	0.0373 (19)	0.0258 (15)	−0.0034 (16)	0.0184 (14)	−0.0009 (16)
C3	0.037 (2)	0.056 (3)	0.026 (2)	0.001 (2)	0.0097 (18)	−0.0002 (19)
C4	0.035 (2)	0.045 (3)	0.0241 (19)	0.001 (2)	0.0049 (17)	−0.002 (2)
C5	0.052 (3)	0.048 (3)	0.043 (3)	0.000 (2)	0.010 (2)	0.004 (2)
C6	0.056 (3)	0.066 (4)	0.049 (3)	0.021 (3)	0.006 (3)	−0.002 (3)
C7	0.034 (3)	0.104 (5)	0.039 (3)	0.003 (3)	0.007 (2)	−0.012 (3)
C8	0.050 (3)	0.078 (4)	0.046 (3)	−0.013 (3)	0.019 (2)	0.001 (3)
C9	0.054 (3)	0.046 (3)	0.047 (3)	0.000 (3)	0.016 (2)	0.004 (2)

Geometric parameters (Å, º)

N11—O1	1.234 (4)	C3—H3A	0.9700
N11—O2	1.254 (4)	C3—H3B	0.9700
N11—O3	1.256 (4)	C4—C9	1.370 (5)
O1A—C1	1.184 (4)	C4—C5	1.372 (6)
O1B—C1	1.308 (4)	C5—C6	1.392 (6)
O1B—H1	0.8200	C5—H5	0.9300
C1—C2	1.533 (5)	C6—C7	1.374 (7)
C2—N1	1.485 (4)	C6—H6	0.9300
C2—C3	1.520 (5)	C7—C8	1.354 (6)
C2—H2	0.9800	C7—H7	0.9300
N1—H1A	0.8900	C8—C9	1.386 (6)
N1—H1B	0.8900	C8—H8	0.9300
N1—H1C	0.8900	C9—H9	0.9300
C3—C4	1.498 (5)
O1—N11—O2	120.3 (4)	C4—C3—H3B	108.1
O1—N11—O3	121.5 (3)	C2—C3—H3B	108.1
O2—N11—O3	118.2 (3)	H3A—C3—H3B	107.3
C1—O1B—H1	109.5	C9—C4—C5	117.8 (4)
O1A—C1—O1B	127.5 (4)	C9—C4—C3	121.3 (4)
O1A—C1—C2	121.5 (3)	C5—C4—C3	120.9 (4)
O1B—C1—C2	111.0 (3)	C4—C5—C6	121.7 (5)
N1—C2—C3	108.6 (3)	C4—C5—H5	119.2
N1—C2—C1	107.7 (3)	C6—C5—H5	119.2
C3—C2—C1	112.0 (3)	C7—C6—C5	119.2 (5)
N1—C2—H2	109.5	C7—C6—H6	120.4
C3—C2—H2	109.5	C5—C6—H6	120.4
C1—C2—H2	109.5	C8—C7—C6	119.7 (4)
C2—N1—H1A	109.5	C8—C7—H7	120.2
C2—N1—H1B	109.5	C6—C7—H7	120.2
H1A—N1—H1B	109.5	C7—C8—C9	120.7 (5)
C2—N1—H1C	109.5	C7—C8—H8	119.7
H1A—N1—H1C	109.5	C9—C8—H8	119.7
H1B—N1—H1C	109.5	C4—C9—C8	121.0 (4)
C4—C3—C2	116.6 (3)	C4—C9—H9	119.5
C4—C3—H3A	108.1	C8—C9—H9	119.5
C2—C3—H3A	108.1
O1A—C1—C2—N1	−34.0 (5)	C9—C4—C5—C6	−1.4 (6)
O1B—C1—C2—N1	145.6 (3)	C3—C4—C5—C6	176.2 (4)
O1A—C1—C2—C3	85.4 (5)	C4—C5—C6—C7	0.9 (6)
O1B—C1—C2—C3	−95.0 (4)	C5—C6—C7—C8	−0.1 (7)
N1—C2—C3—C4	−174.7 (3)	C6—C7—C8—C9	−0.2 (7)
C1—C2—C3—C4	66.5 (5)	C5—C4—C9—C8	1.1 (6)
C2—C3—C4—C9	−101.3 (5)	C3—C4—C9—C8	−176.5 (4)
C2—C3—C4—C5	81.2 (4)	C7—C8—C9—C4	−0.3 (7)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1B—H1···O3	0.82	1.89	2.666 (4)	157
N1—H1A···O1A^i	0.89	1.99	2.841 (4)	160
N1—H1B···O3^ii	0.89	2.07	2.934 (4)	163
N1—H1C···O2^iii	0.89	2.05	2.898 (4)	159

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