(Bromo­meth­yl)trimethyl­ammonium bromide

In the title compound, C₄H₁₁BrN⁺·Br⁻, both ions lie on crystallographic mirror planes. The C...Br distance is 1.943 (4) Å.

Key indicators

• Single-crystal X-ray study
• T = 115 K
• Mean [sigma](N-C) = 0.005 Å
• R factor = 0.038
• wR factor = 0.114
• Data-to-parameter ratio = 23.5

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT431_ALERT_2_B Short Inter HL..A Contact  Br1    ..  Br2     ..       3.37 Ang.

Alert level C
ABSTM02_ALERT_3_C  The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
            Tmin and Tmax reported:      0.148     0.626
            Tmin and Tmax expected:      0.098     0.597
            RR =      1.447
            Please check that your absorption correction is appropriate.
PLAT060_ALERT_3_C Ratio Tmax/Tmin (Exp-to-Rep) (too) Large .......       1.46
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.95
PLAT164_ALERT_4_C Nr. of Refined C-H H-Atoms in Heavy-At Struct...          6

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Recently, we reported our interest in the fundamental structure of halomethyltrimethyl ammonium salts (Fletcher Claville et al., 2006), due to our interest in potential radical reactivity of these and analagous salts (Yates et al.,1984; Rios et al., 1996; Budzinski & Box, 1971; Minegishi, 1977; Stirk & Kenttamaa, 1991; Stirk et al., 1992; Chyall & Kenttamaa, 1994; Della & Smith, 2000). Halomethyltrialkylammonium halides, a specific genre of these salts, are known to perform Grob-like fragmentation reactions (Fig. 1) to produce the corresponding iminium salt and the alkyl halide (Fletcher et al.,1999). These two very different types of reactions from similar types of salts further promote our continued interest in the fundamental structure of these quaternary ammonium salts. Accordingly, we now report the structure for (bromomethyl)trimethylammonium bromide.

Both cation and anion lie on mirror planes. Thus, the conformation of the cation is such that the bromo substituent is exactly anti to a methyl group. The two independent CH₂—N—CH₃ angles differ by 5.9 (4)°, with the in-plane angle, anti to Br, being smaller (Table 1). This effect was also seen in the structure of the BF₄^- salt of this cation (Fletcher Claville et al., 2006), where the difference was 4.8 (2)°.

The ionic packing is illustrated in Fig. 3. Of particular interest are the contacts between the bromide anion and the closest methyl group, due to the resulting demethylation and iminium formation that occurs with heating. Methyl group C3 has a C···Br distance 3.809 (3) Å to Br2 at x, 1/2 - y, z. Methyl group C2 has C···Br distance 3.821 (2) Å to Br2 at x, 1/2 - y, z and a distance of 3.862 (4) Å to Br2 at 1 - x, 1 - y, 1 - z. There is also a short contact between the cation bromo atom and the bromide ion, Br1···Br2(3/2 - x, 1 - y, z - 1/2), 3.369 (1) Å. These interactions are illustrated in Fig. 2.

Structures of three other salts of the (chloromethyl)trimethylammonium ion have been reported (Willey et al., 1991; Johnson et al., 1993; Sieker et al., 1996), as well as the BF₄^- salt of (bromomethyl)trimethylammonium cation (Fletcher Claville et al., 2006).

Related literature

For related literature, see: Budzinski & Box (1971); Chyall & Kenttamaa (1994); Della & Smith (2000); Fletcher et al. (1999); Fletcher, Claville, Payne & Fronczek (2006); Johnson et al. (1993); Minegishi (1977); Rios et al. (1996); Sieker et al. (1996); Stirk & Kenttamaa (1991); Stirk et al. (1992); Willey et al. (1991); Yates et al. (1984).

S2. Experimental

A 50 ml gas capturing flask that was first evacuated and cooled in a dry ice/2-propanol bath (-20°C), was charged with 1.89 g (0.032 mol) anhydrous trimethylamine gas. The trimethylamine gas was then dissolved with 10 ml of ethyl acetate. A 50 ml, 3 necked, round bottom flask that was fitted with a 25 ml-, pressure-equalizing addition funnel and a dry ice condenser, was charged with 10 ml dibromomethane. The flask was then cooled with a dry ice/2-propanol bath (-20°C). THe trimethylamine solution was added dropwise to the flask via the addition funnel over 10 min, with stirring. After allowing the reaction mixture to stir and warm over 24 hr, crude bromomethyltri- methyl ammonium bromide was produced and filtered from the product mixture using vacuum filtration. The pure product was obtained in 69.8% yield after recrystall- ization from ethanol. m.p. 161–3°C (decomp).

S3. Refinement

H-atom positions were refined, resulting in C–H bond distances 0.94 (4) - 0.98 (3) Å. Displacement parameters for H atoms were assigned as either U_iso = 1.2Ueq (CH₂) or 1.5Ueq (CH₃) of the attached C. The largest difference map peak is 0.72 Å from Br2, while the deepest hole is 0.71 Å from Br2.

Computing details

Data collection: COLLECT (Nonius, 2000); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: SCALEPACK and DENZO (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Preparation of bromomethyltrimethylammonium bromide.
	Fig. 2. Structure of (I), showing the atom-numbering scheme and displacement ellipsoids at the 50% probability level.
	Fig. 3. The unit cell, viewed approximately down the c axis, showing closest contacts to the bromide ion. H atoms are not shown.

(Bromomethyl)trimethylammonium bromide

Crystal data

C4H11BrN^+·Br^−	F(000) = 448
Mr = 232.96	Dx = 1.989 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 1506 reflections
a = 19.674 (3) Å	θ = 2.5–31.5°
b = 6.9319 (11) Å	µ = 10.32 mm^−1
c = 5.7038 (10) Å	T = 115 K
V = 777.9 (2) Å^3	Plate, colorless
Z = 4	0.30 × 0.20 × 0.05 mm

Data collection

Nonius KappaCCD diffractometer with an Oxford Cryosystems Cryostream cooler	1363 independent reflections
Radiation source: fine-focus sealed tube	1149 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
ω scans with κ offsets	θmax = 31.5°, θmin = 3.6°
Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor 1997)	h = −28→28
Tmin = 0.148, Tmax = 0.626	k = −10→10
14337 measured reflections	l = −8→8

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.038	Only H-atom coordinates refined
wR(F^2) = 0.114	w = 1/[σ^2(Fo^2) + (0.0802P)^2 + 0.1483P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max = 0.001
1363 reflections	Δρmax = 1.73 e Å^−3
58 parameters	Δρmin = −1.34 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0071 (14)

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
Br1	0.75330 (2)	0.2500	0.55461 (9)	0.02202 (18)
Br2	0.58280 (2)	0.7500	0.88378 (7)	0.01593 (17)
N1	0.60677 (18)	0.2500	0.5040 (6)	0.0132 (6)
C1	0.6621 (2)	0.2500	0.6853 (8)	0.0167 (8)
H1A	0.658 (2)	0.131 (5)	0.775 (5)	0.020*
C2	0.5417 (2)	0.2500	0.6398 (8)	0.0177 (8)
H2A	0.538 (2)	0.360 (5)	0.737 (6)	0.027*
H2B	0.507 (3)	0.2500	0.527 (10)	0.027*
C3	0.61043 (17)	0.0733 (5)	0.3522 (6)	0.0187 (6)
H3A	0.611 (2)	−0.039 (6)	0.455 (7)	0.028*
H3B	0.654 (2)	0.075 (7)	0.271 (5)	0.028*
H3C	0.573 (2)	0.084 (7)	0.251 (7)	0.028*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0145 (2)	0.0227 (3)	0.0289 (3)	0.000	−0.00021 (16)	0.000
Br2	0.0200 (3)	0.0131 (2)	0.0147 (2)	0.000	−0.00118 (14)	0.000
N1	0.0153 (16)	0.0114 (15)	0.0128 (15)	0.000	0.0016 (12)	0.000
C1	0.0155 (18)	0.020 (2)	0.0147 (17)	0.000	−0.0010 (15)	0.000
C2	0.0183 (19)	0.019 (2)	0.0159 (18)	0.000	0.0005 (16)	0.000
C3	0.0263 (15)	0.0138 (13)	0.0160 (12)	−0.0010 (12)	0.0035 (11)	−0.0042 (12)

Geometric parameters (Å, º)

Br1—C1	1.943 (4)	C2—H2A	0.95 (4)
N1—C2	1.496 (5)	C2—H2B	0.94 (6)
N1—C3^i	1.502 (4)	C3—H3A	0.97 (4)
N1—C3	1.502 (4)	C3—H3B	0.97 (4)
N1—C1	1.502 (5)	C3—H3C	0.94 (4)
C1—H1A	0.98 (3)
C2—N1—C3^i	109.8 (2)	N1—C2—H2A	112 (3)
C2—N1—C3	109.8 (2)	N1—C2—H2B	105 (4)
C3^i—N1—C3	109.3 (3)	H2A—C2—H2B	110 (3)
C2—N1—C1	105.3 (3)	N1—C3—H3A	108 (2)
C3^i—N1—C1	111.2 (2)	N1—C3—H3B	108 (3)
C3—N1—C1	111.2 (2)	H3A—C3—H3B	107 (4)
N1—C1—Br1	113.9 (3)	N1—C3—H3C	105 (3)
N1—C1—H1A	107 (2)	H3A—C3—H3C	116 (4)
Br1—C1—H1A	106 (2)	H3B—C3—H3C	113 (3)
C2—N1—C1—Br1	180.0	C3—N1—C1—Br1	61.1 (2)
C3^i—N1—C1—Br1	−61.1 (2)

Symmetry code: (i) x, −y+1/2, z.