3-Chloro-N,N-di­methyl­propan-1-aminium chloride

Bond, M.R.; Silwal, S.

doi:10.1107/S2414314623000159

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 8| Part 1| January 2023| x230015

https://doi.org/10.1107/S2414314623000159

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3-Chloro-N,N-dimethylpropan-1-aminium chloride

Marcus R. Bond ^a ^* and Sajan Silwal ^a

^aDepartment of Chemistry and Physics, Southeast Missouri State University, Cape Girardeau, MO 63701, USA
^*Correspondence e-mail: mbond@semo.edu

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 30 December 2022; accepted 5 January 2023; online 10 January 2023)

The organic cation in the title molecular salt, C₅H₁₃NCl⁺·Cl⁻, exhibits the gauche effect with a C—H bond of the C atom β to the chloro group donating electrons to the antibonding orbital of the C—Cl bond to stabilize the gauche conformation [Cl—C—C—C = −68.6 (6)°], as confirmed by DFT geometry optimizations that show a lengthening of the C—Cl bond relative to that of the anti conformation. Of further interest is the higher point group symmetry of the crystal ( $[\overline{4}]$ ), compared that of the that of the molecular cation, which arises from a supramolecular head-to-tail square arrangement of four molecular cations that circulate in a counterclockwise direction when viewed down the tetragonal c axis.

Keywords: crystal structure; gauche effect; merohedral twin; supramolecular; hyperconjugation.

CCDC reference: 2234390

Structure description

The molecular structure of the title compound, C₅H₁₃NCl⁺·Cl⁻, Fig. 1, corresponds to expected values with an average C—C bond length of 1.497 (8), an average C—N bond length of 1.482 (6) and a C—Cl bond length of 1.781 (7) Å. The bond angles for the sp³ hybridized centers range from 108.7 (4)° to 113.5 (4)°. The Cl atom appears in a gauche conformation, with a Cl1—C1—C2—C3 torsion angle of −68.6 (6)°, rather than in the anti conformation. The structure of the chloroethyl analog (Muller et al., 2021 ; CSD refcode: URORUR) shows an anti conformation for the chloro group (and a disordered alkyl chain) in a lower symmetry space group than the title compound (monoclinic I2/a). We were curious if the gauche conformation was a consequence of packing in the tetragonal space group or a property of the isolated molecule, and pursued a complementary computational study.

Figure 1
Displacement ellipsoid plot (50% level) of the formula unit of the title compound with labels for non-H atoms. H atoms are drawn as circles of arbitrary radii.

A DFT geometry optimization [B3LYP, 6311+G(d,p); GAMESS (Schmidt et al., 1993 )] in vacuo of the gauche conformation similar to that found in the title structure yields a torsion angle of −63.1° and a C—Cl bond length of 1.812 Å, while geometry optimization of the other gauche position yields a torsion angle and bond length of 64.5° and 1.813 Å, respectively, with a slightly lower energy (by 0.0101 eV). In contrast, geometry optimization for the anti conformation yields a shorter C—Cl bond length (1.801 Å) and a higher energy (by 0.0944 eV). For the chloroethyl analog, the gauche conformations are also more stable (by 0.226 eV) than the anti with a similar C—Cl bond lengthening (1.811 Å versus 1.795 Å). These results are consistent with hyperconjugation, which places a β-H atom in an anti-periplanar arrangement with Cl, i.e. the gauche effect. This anti-periplanar arrangement allows the back donation of the β C—H bond electrons to the anti-bonding molecular orbital of the C—Cl bond with resulting C—Cl bond lengthening (Wolfe, 1972 ; Rodrigues Silva et al., 2021 ). Furthermore, the gauche conformation also places the partially negative Cl atom and formally positive N atom in proximity to enhance stability, as shown in the electrostatic potential plot of Fig. 2. This agrees with calculated Cl⋯N distances of 4.60 Å [gauche, 4.638 (4) Å, experimental] versus 5.27 Å (anti) for the title compound and, likewise, 3.07 versus 4.10 Å for the chloroethyl analog. With the greater calculated stabilization of the gauche conformation in the chloroethyl analog, it is surprising to see the anti conformation in URORUR. It is worth noting, though, that a gauche conformation is found for this cation in the hexachlorodioxodimolybdate(V) salt (POSWAX) with an ordered alkyl chain (Marchetti et al., 2015 ).

Figure 2
Electrostatic potential plot of the molecular cation in the title compound from the reported DFT calculation. Red represents the most negatively charged regions and blue the most positively charged regions.

The extended structure of the title compound can be envisioned as layers of ion-pair formula units lying parallel to ab, shown in Fig. 3, with the structure built up by offset stacking of these layers along c due to the I centering translation. Within the layer, two motifs catch the eye as representative of $[\overline{4}]$ symmetry. One is a pinwheel structure in which the ends of the propyl chains of four organic cations meet at the center. Chloro groups at the center are directed above or below the layer plane with alternating orientations as one progresses around the pinwheel (Fig. 4). The other motif is a square with a formula unit on each edge in a head-to-tail arrangement with the chloride ion close to the ammonium head group on each edge (Fig. 5). The head-to-tail arrangement circulates in a counterclockwise direction looking down c. Application of a twofold rotation perpendicular to c generates the other twin component in which the sense of circulation is reversed. The square motif contains a void in the center about which the chloro groups from pinwheel motifs of neighboring layers, a pair from each arranged in a distorted tetrahedron, fit. The H atom of the ammonium group has the opposite orientation to the chloro group and hydrogen bonds to a chloride ion of the other neighbor layer (Table 1). Thus the only classical hydrogen bonding is interlayer. A packing diagram with unit cell axes is shown in Fig. 6.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯Cl01	0.98	2.05	3.032 (3)	177

Figure 3
Ball-and-stick diagram of a portion of the layer in the ab plane. The three-dimensional structure is generated by offset stacking of these layers in the c-axis direction.

Figure 4
Ball-and-stick diagram of the pinwheel structural motif found in the layer depicted in Fig. 3

Figure 5
Ball-and-stick diagram of the square structural motif found in the layer depicted in Fig. 3

Figure 6
Capped-stick packing diagram for the title compound showing the sequential offset stacking of three layers and the interlayer hydrogen bonding that connects neighboring layers.

Synthesis and crystallization

Crystalline 3-chloro-N,N-dimethylpropan-1-aminium chloride, 99% (CAS 5407–04-5) was purchased from Acros Organics and used as received.

Refinement

All non-H atoms were found during initial structure solution and refined anisotropically. A check using the PLATON routine TwinRotMat (Spek, 2020 ) suggested merohedral twinning about a twofold axis in the higher symmetry tetragonal point group $[\overline{4}]$ 2m. Refinement of the twin model [BASF = 0.358 (2) for the minor component] resulted in a substantial drop in R-factor values, rectification of highly anomalous displacement ellipsoids, and the appearance of H atoms in the electron-density difference map. Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	C₅H₁₃NCl⁺·Cl⁻
M_r	158.06
Crystal system, space group	Tetragonal, I $[\overline{4}]$
Temperature (K)	295
a, c (Å)	15.9302 (8), 6.9779 (4)
V (Å³)	1770.8 (2)
Z	8
Radiation type	Mo Kα
μ (mm⁻¹)	0.65
Crystal size (mm)	0.33 × 0.33 × 0.28

Data collection
Diffractometer	Bruker D8 Quest Eco
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.96, 1.00
No. of measured, independent and observed [I > 2σ(I)] reflections	27888, 2028, 1731
R_int	0.045
(sin θ/λ)_max (Å⁻¹)	0.650

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.039, 0.085, 1.09
No. of reflections	2028
No. of parameters	77
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.17, −0.21
Absolute structure	Flack x determined using 668 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] (Parsons et al., 2013 ).
Absolute structure parameter	0.14 (3)
Computer programs: APEX3 and SAINT (Bruker, 2017 ), SHELXT2014/5 (Sheldrick, 2015a ), SHELXL2016/6 (Sheldrick, 2015b ), ShelXle (Hübschle et al., 2011 ), ORTEP-3 for Windows (Farrugia, 2012 ), Mercury (MacCrae et al., 2020 ), and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2234390

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2414314623000159/hb4422sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314623000159/hb4422Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314623000159/hb4422Isup3.cml

checkCIF report

Computing details top

Data collection: APEX3 (Bruker,2017); cell refinement: SAINT (Bruker, 2017); data reduction: SAINT (Bruker, 2017); program(s) used to solve structure: SHELXT2014/5 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016/6 (Sheldrick, 2015b); molecular graphics: ShelXle (Hübschle et al., 2011), ORTEP-3 for Windows (Farrugia, 2012), Mercury (MacCrae et al., 2020); software used to prepare material for publication: publCIF (Westrip, 2010).

3-Chloro-N,N-dimethylpropan-1-aminium chloride top

Crystal data top

C₅H₁₃NCl⁺·Cl⁻	D_x = 1.186 Mg m⁻³
M_r = 158.06	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4	Cell parameters from 9912 reflections
a = 15.9302 (8) Å	θ = 3.2–24.4°
c = 6.9779 (4) Å	µ = 0.65 mm⁻¹
V = 1770.8 (2) Å³	T = 295 K
Z = 8	Gem, colourless
F(000) = 672	0.33 × 0.33 × 0.28 mm

Data collection top

Bruker D8 Quest Eco diffractometer	1731 reflections with I > 2σ(I)
Detector resolution: 10.4167 pixels mm^-1	R_int = 0.045
φ and ω scans	θ_max = 27.5°, θ_min = 3.6°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −20→20
T_min = 0.96, T_max = 1.00	k = −20→20
27888 measured reflections	l = −9→9
2028 independent reflections

Refinement top

Refinement on F²	H-atom parameters constrained
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0448P)² + 0.267P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.039	(Δ/σ)_max < 0.001
wR(F²) = 0.085	Δρ_max = 0.17 e Å⁻³
S = 1.09	Δρ_min = −0.21 e Å⁻³
2028 reflections	Extinction correction: SHELXL2016/6 (Sheldrick 2015b)
77 parameters	Extinction coefficient: 0.0065 (14)
0 restraints	Absolute structure: Flack x determined using 668 quotients [(I+)-(I-)]/[(I+)+(I-)] [(I⁺)-(I^-)]/[(I⁺)+(I^-)] (Parsons et al., 2013).
Primary atom site location: dual	Absolute structure parameter: 0.14 (3)
Hydrogen site location: inferred from neighbouring sites

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.

Refinement. Refined as a 2-component twin.

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

	x	y	z	U_iso*/U_eq
Cl01	0.65850 (7)	0.63178 (7)	0.29014 (15)	0.0535 (3)
Cl1	0.56868 (10)	0.87927 (9)	0.9901 (3)	0.0929 (5)
N1	0.6590 (2)	0.6289 (2)	0.7246 (4)	0.0438 (6)
H1A	0.660711	0.6302	0.584228	0.053*
C1	0.5994 (4)	0.8605 (3)	0.7485 (9)	0.0787 (18)
H9	0.563704	0.893086	0.663944	0.094*
H10	0.656665	0.879864	0.730952	0.094*
C2	0.5942 (3)	0.7698 (3)	0.6928 (9)	0.0630 (12)
H2A	0.538666	0.748719	0.723186	0.076*
H2B	0.602098	0.76485	0.555387	0.076*
C3	0.6582 (3)	0.7171 (3)	0.7925 (9)	0.0560 (10)
H3A	0.713328	0.741437	0.772339	0.067*
H3B	0.646958	0.717718	0.929063	0.067*
C4	0.5832 (3)	0.5807 (3)	0.7811 (9)	0.0567 (11)
H4	0.576969	0.582365	0.917864	0.085*
H1	0.589026	0.523441	0.740045	0.085*
H5	0.534541	0.605002	0.721853	0.085*
C5	0.7342 (3)	0.5829 (4)	0.7906 (9)	0.0758 (15)
H7	0.783783	0.612619	0.751482	0.114*
H8	0.734577	0.527686	0.735402	0.114*
H6	0.733241	0.578483	0.927797	0.114*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cl01	0.0658 (7)	0.0641 (7)	0.0305 (3)	−0.0131 (6)	−0.0017 (5)	0.0007 (5)
Cl1	0.0831 (9)	0.0854 (9)	0.1101 (12)	0.0024 (7)	−0.0101 (11)	−0.0249 (10)
N1	0.0472 (19)	0.056 (2)	0.0280 (12)	0.0004 (19)	0.0029 (17)	0.0020 (15)
C1	0.076 (3)	0.061 (3)	0.099 (5)	−0.004 (2)	−0.008 (3)	0.019 (3)
C2	0.071 (3)	0.065 (3)	0.053 (3)	−0.001 (2)	−0.009 (3)	0.005 (3)
C3	0.064 (2)	0.057 (2)	0.0471 (19)	−0.009 (2)	−0.003 (2)	0.006 (2)
C4	0.058 (3)	0.053 (2)	0.060 (2)	−0.0108 (19)	0.002 (3)	0.004 (3)
C5	0.059 (3)	0.112 (4)	0.056 (2)	0.024 (3)	0.002 (3)	0.003 (4)

Geometric parameters (Å, º) top

Cl1—C1	1.781 (7)	C2—H2B	0.97
N1—C5	1.479 (6)	C3—H3A	0.97
N1—C3	1.483 (6)	C3—H3B	0.97
N1—C4	1.484 (6)	C4—H4	0.96
N1—H1A	0.98	C4—H1	0.96
C1—C2	1.500 (8)	C4—H5	0.96
C1—H9	0.97	C5—H7	0.96
C1—H10	0.97	C5—H8	0.96
C2—C3	1.493 (7)	C5—H6	0.96
C2—H2A	0.97

C5—N1—C3	112.1 (4)	N1—C3—C2	112.9 (4)
C5—N1—C4	108.7 (4)	N1—C3—H3A	109.0
C3—N1—C4	113.5 (4)	C2—C3—H3A	109.0
C5—N1—H1A	107.4	N1—C3—H3B	109.0
C3—N1—H1A	107.4	C2—C3—H3B	109.0
C4—N1—H1A	107.4	H3A—C3—H3B	107.8
C2—C1—Cl1	113.1 (4)	N1—C4—H4	109.5
C2—C1—H9	109.0	N1—C4—H1	109.5
Cl1—C1—H9	109.0	H4—C4—H1	109.5
C2—C1—H10	109.0	N1—C4—H5	109.5
Cl1—C1—H10	109.0	H4—C4—H5	109.5
H9—C1—H10	107.8	H1—C4—H5	109.5
C3—C2—C1	112.6 (5)	N1—C5—H7	109.5
C3—C2—H2A	109.1	N1—C5—H8	109.5
C1—C2—H2A	109.1	H7—C5—H8	109.5
C3—C2—H2B	109.1	N1—C5—H6	109.5
C1—C2—H2B	109.1	H7—C5—H6	109.5
H2A—C2—H2B	107.8	H8—C5—H6	109.5

Cl1—C1—C2—C3	−68.6 (6)	C4—N1—C3—C2	−69.5 (6)
C5—N1—C3—C2	166.9 (5)	C1—C2—C3—N1	−174.5 (4)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···Cl01	0.98	2.05	3.032 (3)	177

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