5-tert-Butyl-3-methyl-1H-pyrazole at 240 K

The title compound, C₈H₁₄N₂, exists in the solid state as a tetramer with hydrogen bonding around the axis.

Key indicators

• Single-crystal X-ray study
• T = 240 K
• Mean [sigma](C-C) = 0.007 Å
• R factor = 0.088
• wR factor = 0.117
• Data-to-parameter ratio = 11.6

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level A:



PLAT_601  Alert A Structure contains solvent accessible VOIDS of     442.00 A   3

Author response: There are four voids in the structure located at (0,0,1/2) and equivalent positions, spherical in shape and of 3.5\%A diameter approximately (Cano & Martinez-Ripoll, 1992). According to the ^1^H and ^13^C NMR experiments no solvent molecules were detected. Futhermore, no residual electron density was found for ordered water. This paragraph has been included in the experimental section

 Alert Level C:



THETM_01  Alert C The value of sine(theta_max)/wavelength is less than 0.590
          Calculated sin(theta_max)/wavelength =    0.5878

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           65.00
         From the CIF: _reflns_number_total               1509
         Count of symmetry unique reflns         1511
         Completeness (_total/calc)             99.87%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured         0
         Fraction of Friedel pairs measured     0.000
         Are heavy atom types Z>Si present           no
          Please check that the estimate of the number of Friedel pairs is
          correct. If it is not, please give the correct count in the
          _publ_section_exptl_refinement section of the submitted CIF.


 1 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

One of our interests in crystalline pyrazoles involves elucidation of factors controlling the four intermolecular hydrogen-bonding modes (catemers, dimers, trimers and tetramers) that have been found in pyrazoles bearing only one conventional donor and/or including other acceptor groups apart from that of the pyrazole (Foces-Foces et al., 2000). In the three 3,5-di-tert-butylpyrazole derivatives studied so far (with substituents at C4═NO₂, H and NO; Llamas-Saiz et al., 1994; Aguilar-Parrilla et al., 1995; Fletcher et al., 1997; CSD refcodes WILBAU, YULNUO and RIVBAZ, respectively), the dimeric association is the only hydrogen-bonding mode observed. The aim of this paper is to study the contribution of different types of substituents on the secondary structure (one methyl group at C3 instead of a tert-butyl group) which appear to govern the choice of a hydrogen-bonding mode.

It is noteworthy that the 5-tert-butyl-3-methyl-1H-pyrazole tautomer, (I), is present in the solid state (Fig. 1) in spite of the tendency of these compounds to present proton disorder. The bond distances and angles in the ring are unremarkable with respect to those of the undisordered proton derivatives and the parent compound (i.e. N2—N1—C5 > N1—N2—C3; N2—C3—C4 > N1—C5—C4). The conformation of the tert-butyl group places the methyl C10 eclipsed with respect to the H4 atom whereas, in the previous reported derivatives with substituents at C4, one methyl group is eclipsed with respect to the the N atoms to avoid steric repulsions (Table 1).

An intermolecular hydrogen bond between the N atoms of the pyrazole (Table 2) leads to the formation of tetramers, around the 4 axis (Figs. 2 and 3), in agreement with the proposed secondary structure model (Foces-Foces et al., 2000) for methyl and butyl substituents at C3 and C5.

S2. Experimental

The title compound was prepared according to López et al. (1993) and crystals were obtained by recrystallization from cyclohexane. The melting point (440 K) was determined by DSC with a Seiko 220 C instrument with a scanning rate of 2° min^-1.

S3. Refinement

Considering the possibility of disorder of the tert-butyl group the data were collected at 240 K using an Oxford Cryostream device (Cosier & Glazer, 1986) and the stated temperature was measured continuously during data collection. Due to the disposition of the low-temperature device, the maximum θ angle available is 65°. Rotational disorder of the tert-butyl group around the C5—C7 bond was apparent from their large displacement parameters; however, attemps to establish a disordered model failed. The highest peaks of 0.39 e Å^-3 in the final difference synthesis are close to the tert-butyl group. All H atoms were obtained from difference Fourier synthesis although only H1 was refined freely; others were constrained. The weighting schemes were established in an empirical way as to give no trends in <wΔ²F> versus <F_o> or <sinθ/λ>, using different parameters in the weighting formula for different ranges of these variables (PESOS; Martínez-Ripoll & Cano, 1975). There are four voids in the structure located at (0,0,1/2) and equivalent positions, spherical in shape and of 3.5 Å diameter approximately (Cano & Martinez-Ripoll, 1992). According to the ¹H and ¹³C NMR experiments no solvent molecules were detected. The calculated density for the title compound is in the range found for the analogous derivatives (WILBAU, YULNUO, RIVBAZ).

Computing details

Data collection: Philips PW1100 (Hornstra & Vossers, 1973); cell refinement: LSUCRE (Appleman, 1984); data reduction: Xtal3.6 ADDREF DIFDAT SORTRF (Hall et al., 1999); program(s) used to solve structure: SIR97 (Altomare et al., 1997); program(s) used to refine structure: Xtal3.6 CRYLSQ; molecular graphics: Xtal3.6; software used to prepare material for publication: Xtal3.6 BONDLA CIFIO.

Figures

	Fig. 1. The molecular structure of (I) showing the numbering scheme. The displacement parameters are drawn at the 30% probability level.
	Fig. 2. The tetrameric arrangement of molecules around the 4 axis. Dotted lines represent hydrogen bond interactions.
	Fig. 3. The crystal packing viewed along the c axis.

(I)

Crystal data

C8H14N2	Dx = 1.034 Mg m^−3
Mr = 138.21	Melting point: 440 K
Tetragonal, I41/a	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: i 4bw -1bw	Cell parameters from 56 reflections
a = 18.2451 (16) Å	θ = 2–45°
c = 10.6667 (8) Å	µ = 0.48 mm^−1
V = 3550.8 (7) Å^3	T = 240 K
Z = 16	Prism, colourless
F(000) = 1216	0.50 × 0.10 × 0.10 mm

Data collection

Philips PW100 diffractometer	θmax = 65.0°, θmin = 4.8°
ω/2θ scans	h = 0→21
1509 measured reflections	k = 0→21
1509 independent reflections	l = 0→12
1100 reflections with I > 2σ(I)	2 standard reflections every 90 min
Rint = 0	intensity decay: 3%

Refinement

Refinement on F	39 restraints
Least-squares matrix: full	0 constraints
R[F^2 > 2σ(F^2)] = 0.088	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.117	w = k/[(A + B Fo)^2(C + D(sinθ)/λ)]
S = 0.98	(Δ/σ)max = 0.005
1100 reflections	Δρmax = 0.39 e Å^−3
95 parameters	Δρmin = −0.31 e Å^−3

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

	x	y	z	Uiso*/Ueq
N1	0.09449 (18)	−0.05360 (17)	0.1151 (3)	0.0460 (17)
N2	0.11979 (18)	0.01379 (18)	0.0895 (3)	0.0488 (17)
C3	0.1543 (2)	0.0360 (2)	0.1941 (4)	0.047 (2)
C4	0.1507 (2)	−0.0196 (2)	0.2839 (3)	0.0465 (18)
C5	0.11229 (19)	−0.0765 (2)	0.2320 (3)	0.0414 (17)
C6	0.1890 (3)	0.1091 (3)	0.2021 (5)	0.066 (3)
C7	0.0867 (2)	−0.1487 (2)	0.2826 (4)	0.053 (2)
C8	0.1125 (6)	−0.2115 (3)	0.1989 (7)	0.103 (5)
C9	0.0034 (4)	−0.1513 (4)	0.2832 (9)	0.107 (5)
C10	0.1156 (5)	−0.1603 (4)	0.4139 (6)	0.106 (5)
H1	0.068 (3)	−0.082 (3)	0.0587 (5)	0.032 (12)*
H4	0.1727	−0.0180	0.3738	0.047*
H6a	0.1564	0.1467	0.1545	0.050*
H6b	0.1942	0.1245	0.2955	0.066*
H6c	0.2408	0.1069	0.1616	0.066*
H8a	0.0882	−0.2066	0.1110	0.066*
H8b	0.1692	−0.2095	0.1900	0.104*
H8c	0.0973	−0.2612	0.2390	0.104*
H9a	−0.0143	−0.2017	0.3170	0.104*
H9b	−0.0161	−0.1441	0.1923	0.107*
H9c	−0.0164	−0.1097	0.3405	0.107*
H10a	0.1004	−0.1164	0.4704	0.107*
H10b	0.0940	−0.2087	0.4501	0.107*
H10c	0.1725	−0.1639	0.4120	0.107*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0526 (17)	0.0477 (17)	0.0377 (16)	−0.0048 (13)	−0.0070 (13)	0.0020 (12)
N2	0.0527 (18)	0.0520 (18)	0.0416 (16)	−0.0052 (13)	−0.0041 (13)	0.0062 (13)
C3	0.0441 (18)	0.049 (2)	0.049 (2)	−0.0001 (14)	−0.0007 (15)	−0.0011 (15)
C4	0.0498 (19)	0.048 (2)	0.0416 (18)	−0.0038 (14)	−0.0069 (15)	0.0015 (15)
C5	0.0434 (17)	0.0443 (18)	0.0366 (17)	0.0030 (13)	−0.0033 (13)	0.0018 (13)
C6	0.073 (3)	0.054 (2)	0.072 (3)	−0.005 (2)	−0.008 (2)	0.002 (2)
C7	0.059 (2)	0.051 (2)	0.048 (2)	−0.0065 (15)	−0.0033 (17)	0.0055 (16)
C8	0.163 (7)	0.053 (3)	0.095 (4)	−0.009 (3)	0.032 (4)	−0.004 (3)
C9	0.072 (3)	0.095 (4)	0.153 (7)	−0.010 (3)	0.005 (4)	0.053 (5)
C10	0.161 (7)	0.085 (4)	0.073 (4)	−0.047 (4)	−0.044 (4)	0.034 (3)

Geometric parameters (Å, º)

N1—H1	0.93 (5)	C7—C10	1.513 (8)
N1—N2	1.342 (5)	C7—C9	1.521 (8)
N1—C5	1.354 (5)	C7—C8	1.527 (8)
N2—C3	1.344 (5)	C8—H8c	1.040
C3—C4	1.396 (5)	C8—H8b	1.040
C3—C6	1.479 (6)	C8—H8a	1.040
C4—H4	1.040	C9—H9a	1.040
C4—C5	1.370 (5)	C9—H9c	1.040
C5—C7	1.498 (5)	C9—H9b	1.040
C6—H6b	1.040	C10—H10a	1.040
C6—H6c	1.040	C10—H10c	1.040
C6—H6a	1.040	C10—H10b	1.040
H1—N1—N2	124 (3)	C10—C7—C9	109.9 (6)
H1—N1—C5	123 (3)	C10—C7—C8	109.2 (5)
N2—N1—C5	112.8 (3)	C9—C7—C8	106.7 (6)
N1—N2—C3	105.5 (3)	H8c—C8—H8b	109.4
N2—C3—C4	109.2 (3)	H8c—C8—H8a	109.4
N2—C3—C6	121.3 (4)	H8c—C8—C7	109.4
C4—C3—C6	129.4 (4)	H8b—C8—H8a	109.8
H4—C4—C5	126.2	H8b—C8—C7	109.5
H4—C4—C3	126.5	H8a—C8—C7	109.4
C5—C4—C3	107.3 (3)	H9a—C9—H9c	109.5
N1—C5—C4	105.1 (3)	H9a—C9—H9b	109.3
N1—C5—C7	121.9 (3)	H9a—C9—C7	109.8
C4—C5—C7	132.9 (3)	H9c—C9—H9b	109.7
H6b—C6—H6c	109.0	H9c—C9—C7	109.0
H6b—C6—H6a	109.9	H9b—C9—C7	109.4
H6b—C6—C3	109.8	H10a—C10—H10c	109.2
H6c—C6—H6a	110.0	H10a—C10—H10b	109.7
H6c—C6—C3	109.2	H10a—C10—C7	109.6
H6a—C6—C3	108.9	H10c—C10—H10b	109.6
C5—C7—C10	110.4 (4)	H10c—C10—C7	109.5
C5—C7—C9	110.0 (4)	H10b—C10—C7	109.3
C5—C7—C8	110.7 (4)
C5—N1—N2—C3	−1.0 (4)	C5—C7—C8—H8a	−64.2
H1—N1—N2—C3	180 (4)	C5—C7—C8—H8b	56.1
N2—N1—C5—C4	0.7 (4)	C5—C7—C8—H8c	176.0
N2—N1—C5—C7	177.1 (3)	C9—C7—C8—H8a	55.4
H1—N1—C5—C4	180 (4)	C9—C7—C8—H8b	175.7
H1—N1—C5—C7	−4 (4)	C9—C7—C8—H8c	−64.4
N1—N2—C3—C4	0.9 (4)	C10—C7—C8—H8a	174.1
N1—N2—C3—C6	−179.2 (4)	C10—C7—C8—H8b	−65.6
N2—C3—C4—C5	−0.5 (4)	C10—C7—C8—H8c	54.3
N2—C3—C4—H4	179.8	C5—C7—C9—H9a	179.1
C6—C3—C4—C5	179.6 (4)	C5—C7—C9—H9b	59.2
C6—C3—C4—H4	−0.1	C5—C7—C9—H9c	−60.8
N2—C3—C6—H6a	37.4	C8—C7—C9—H9a	59.1
N2—C3—C6—H6b	157.8	C8—C7—C9—H9b	−60.9
N2—C3—C6—H6c	−82.7	C8—C7—C9—H9c	179.1
C4—C3—C6—H6a	−142.7	C10—C7—C9—H9a	−59.1
C4—C3—C6—H6b	−22.3	C10—C7—C9—H9b	−179.1
C4—C3—C6—H6c	97.1	C10—C7—C9—H9c	60.9
C3—C4—C5—N1	−0.1 (4)	C5—C7—C10—H10a	55.4
C3—C4—C5—C7	−175.9 (4)	C5—C7—C10—H10b	175.6
H4—C4—C5—N1	179.7	C5—C7—C10—H10c	−64.4
H4—C4—C5—C7	3.8	C8—C7—C10—H10a	177.2
N1—C5—C7—C8	58.2 (6)	C8—C7—C10—H10b	−62.5
N1—C5—C7—C9	−59.4 (6)	C8—C7—C10—H10c	57.5
N1—C5—C7—C10	179.2 (5)	C9—C7—C10—H10a	−66.1
C4—C5—C7—C8	−126.5 (6)	C9—C7—C10—H10b	54.1
C4—C5—C7—C9	115.9 (6)	C9—C7—C10—H10c	174.2
C4—C5—C7—C10	−5.5 (7)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···N2^i	0.93 (5)	1.99 (6)	2.896 (5)	165 (5)

Symmetry code: (i) y, −x, −z.