1-Ethynyl-2-isopropoxy-3-methoxy­benzene

The crystal structure of the title compound, C₁₂H₁₄O₂, has been determined at 150 K. Significant intermolecular non-conventional C—H...O interactions involving the terminal acetyl­inic H atom are observed, which result in a zigzag hydrogen-bonded chain in the b direction.

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.039
• wR factor = 0.112
• Data-to-parameter ratio = 14.1

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



PLAT_371  Alert C Long   C(sp2)-C(sp1) Bond  C(1)   -   C(7)   =       1.44 Ang.

PLAT_710  Alert C Delete 1-2-3 or 2-3-4 (CIF) Linear Torsion Angle #     15
                   C2  -C1  -C7  -C8   -164.00  3.00   1.555   1.555   1.555   1.555

PLAT_710  Alert C Delete 1-2-3 or 2-3-4 (CIF) Linear Torsion Angle #     16
                   C6  -C1  -C7  -C8     16.00  4.00   1.555   1.555   1.555   1.555


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 3 Alert Level C = Please check

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S1. Comment

In our quest for developing direct synthetic routes towards the total synthesis of certain diterpene alkaloids (Atta-ur-Rahman & Choudhary, 1997, 1999; Wang & Liang, 1992), we required 1,2-dioxygenated phenylacetylenes as masked o-benzoquinones (Liao & Peddinti, 2002). In particular, we have made use of 1-ethynyl-2-isopropoxy-3-methoxybenzene, (I), which is easily synthesized on large scale (> 20 g) in three steps from o-vanillin, (II) (Williams et al., 2003).

Crystallographic data for (I) were collected at 150 K due to the low melting point of the compound (321–323 K, uncorrected). The molecular structure of (I) is shown in Fig. 1. The methoxy group lies esentially in the plane of the phenyl ring [C4—C3—O2—C12 = 3.2 (2)°], whereas the isopropoxyl group C9—O1 vector is rotated well away from this plane [C3—C2—O1—C9 = 71.5 (2)°]. The bond lengths and angles (Table 1) are as expected for a purely organic phenylacetylene, of which there are 574 structurally characterized examples in the Cambridge Structural Database (Allen, 2002); 61 bearing a terminal (monosubstituted) acetylene group. The C1—C7 distance of 1.441 (2) Å (formally a single bond) reflects conjugation between the phenyl ring and the alkyne group. Nevertheless, this bond length is not significantly different from that seen in other phenylacetylenes. Interestingly, there are an additional 1407 metal-containing structures where the phenylacetylene moiety is coordinated as either an η¹ σ-donor (in its deprotonated form) or in a side-on η²-bonding mode as a neutral ligand. The most closely related crystal structures to (I) are those of the 2–6-dioxyphenylacetylenes (III) (Evans et al., 1990) and (IV) (Evans et al., 1989). The present crystal structure of (I) represents the first example of a 2,3-dioxyphenylacetylene in the literature.

There is a non-classical intermolecular hydrogen-bonding interaction involving the acetylinic proton and the isopropoxyl group [H8···O1ⁱ 2.31 Å, C8···O1ⁱ 3.233 (2) Å and C8—H8···O1ⁱ 169.6 (1)°; symmetry code: (i) −x + 3/2, y − 1/2, z]. This results in an hydrogen-bonded chain of molecules in the b direction (Fig. 2). A weaker intramolecular C—H···O interaction occurs between the isopropoxyl methine proton and the adjacent methoxyl group [H9···O2 2.44 Å, C9···O2 3.026 (2) Å and C9—H9···O2 117.6 (1)°]. An avoidance of steric repulsion between the isopropoxyl and methoxyl methyl groups may also be significant in assisting this non-conventional hydrogen-bonding interaction. Moreover, the above-mentioned intermolecular hydrogen bond with H8 will be important in influencing the orientation of the isopropoxyl group.

We are currently employing this useful synthon (I) in the pursuit of a number of novel polycyclic organic derivatives and we shall report the results of these investigations separately (Williams et al., 2003).

S2. Experimental

The synthesis of the title compound will be reported separately in a full account (Williams et al., 2003). Following distillation, (I) crystallized upon cooling to room temperature.

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS86 (Sheldrick, 1985); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. ORTEP-3 plot (Farrugia, 1997) of (I) (30% probability ellipsoids).
	Fig. 2. PLUTON packing diagram (Spek, 1990) showing hydrogen-bonded chains. All H atoms, except for the acetylinic proton, have been omitted and C8 has been highlighted in a different shading from the remaining C atoms.

(I)

Crystal data

C12H14O2	F(000) = 816
Mr = 190.23	Dx = 1.198 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 25 reflections
a = 9.895 (1) Å	θ = 11.2–14.2°
b = 11.343 (2) Å	µ = 0.08 mm^−1
c = 18.791 (2) Å	T = 150 K
V = 2109.1 (5) Å^3	Prism, colourless
Z = 8	0.5 × 0.5 × 0.3 mm

Data collection

Enraf-Nonius TurboCAD4 diffractometer	Rint = 0.037
Radiation source: Enraf Nonius FR590	θmax = 25.0°, θmin = 2.2°
Graphite monochromator	h = −1→11
non–profiled ω/2θ scans	k = −1→13
2431 measured reflections	l = −1→22
1847 independent reflections	3 standard reflections every 120 min
1368 reflections with I > 2σ(I)	intensity decay: 1%

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)] = 0.039	H-atom parameters constrained
wR(F^2) = 0.112	w = 1/[σ^2(Fo^2) + (0.0619P)^2 + 0.4832P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
1847 reflections	Δρmax = 0.22 e Å^−3
131 parameters	Δρmin = −0.23 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: 0.0097 (15)

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
C1	0.54112 (16)	0.19490 (14)	0.57991 (8)	0.0223 (4)
C2	0.51895 (16)	0.30191 (14)	0.61453 (8)	0.0211 (4)
C3	0.43349 (17)	0.38615 (14)	0.58391 (8)	0.0232 (4)
C4	0.36924 (18)	0.36175 (15)	0.51998 (9)	0.0286 (4)
H4	0.3107	0.4168	0.5001	0.034*
C5	0.39235 (19)	0.25522 (15)	0.48573 (9)	0.0303 (4)
H5	0.3491	0.2394	0.4428	0.036*
C6	0.47786 (18)	0.17337 (14)	0.51433 (8)	0.0273 (4)
H6	0.4942	0.1032	0.4903	0.033*
C7	0.62784 (17)	0.10692 (14)	0.61118 (8)	0.0247 (4)
C8	0.69953 (18)	0.03208 (16)	0.63409 (9)	0.0307 (4)
H8	0.7557	−0.0266	0.652	0.037*
C9	0.50921 (18)	0.33300 (14)	0.74135 (8)	0.0256 (4)
H9	0.4364	0.3906	0.735	0.031*
C10	0.4487 (2)	0.21431 (17)	0.75864 (9)	0.0362 (5)
H10A	0.3932	0.1886	0.7197	0.054*
H10B	0.3945	0.2206	0.8009	0.054*
H10C	0.5198	0.1582	0.7664	0.054*
C11	0.6057 (2)	0.37719 (16)	0.79715 (8)	0.0332 (4)
H11A	0.6801	0.3234	0.8014	0.05*
H11B	0.5597	0.3829	0.842	0.05*
H11C	0.6389	0.4535	0.7837	0.05*
C12	0.3300 (2)	0.57492 (15)	0.59057 (10)	0.0349 (5)
H12A	0.3599	0.5965	0.5437	0.052*
H12B	0.3282	0.6436	0.6204	0.052*
H12C	0.241	0.5416	0.5878	0.052*
O1	0.58896 (11)	0.32627 (10)	0.67607 (5)	0.0230 (3)
O2	0.42065 (13)	0.49027 (10)	0.61993 (6)	0.0305 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0213 (9)	0.0220 (8)	0.0235 (8)	−0.0025 (7)	0.0037 (7)	0.0043 (7)
C2	0.0191 (8)	0.0249 (8)	0.0193 (8)	−0.0030 (7)	0.0003 (7)	0.0026 (6)
C3	0.0249 (9)	0.0219 (8)	0.0227 (8)	−0.0007 (7)	0.0002 (7)	0.0007 (7)
C4	0.0277 (10)	0.0302 (9)	0.0280 (9)	0.0033 (8)	−0.0046 (8)	0.0041 (7)
C5	0.0344 (10)	0.0349 (9)	0.0215 (9)	−0.0034 (8)	−0.0051 (7)	0.0000 (7)
C6	0.0314 (10)	0.0253 (9)	0.0253 (8)	−0.0026 (8)	0.0019 (7)	−0.0013 (7)
C7	0.0257 (9)	0.0257 (8)	0.0228 (8)	−0.0015 (8)	0.0056 (7)	−0.0007 (7)
C8	0.0327 (10)	0.0300 (9)	0.0294 (9)	0.0067 (9)	0.0037 (8)	0.0041 (7)
C9	0.0261 (9)	0.0298 (9)	0.0209 (8)	0.0048 (7)	0.0013 (7)	0.0011 (7)
C10	0.0392 (11)	0.0431 (10)	0.0263 (9)	−0.0102 (9)	0.0043 (8)	0.0033 (8)
C11	0.0394 (10)	0.0350 (10)	0.0251 (9)	−0.0001 (9)	−0.0028 (8)	−0.0007 (8)
C12	0.0414 (11)	0.0274 (9)	0.0360 (9)	0.0103 (9)	−0.0040 (9)	0.0029 (7)
O1	0.0214 (6)	0.0276 (6)	0.0201 (6)	−0.0018 (5)	−0.0022 (5)	0.0010 (5)
O2	0.0374 (7)	0.0237 (6)	0.0305 (7)	0.0072 (5)	−0.0071 (6)	−0.0006 (5)

Geometric parameters (Å, º)

C1—C2	1.395 (2)	C9—O1	1.461 (2)
C1—C6	1.404 (2)	C9—C11	1.504 (2)
C1—C7	1.441 (2)	C9—C10	1.509 (2)
C2—O1	1.376 (2)	C9—H9	0.9800
C2—C3	1.400 (2)	C10—H10A	0.9600
C3—O2	1.367 (2)	C10—H10B	0.9600
C3—C4	1.387 (2)	C10—H10C	0.9600
C4—C5	1.388 (2)	C11—H11A	0.9600
C4—H4	0.9300	C11—H11B	0.9600
C5—C6	1.366 (2)	C11—H11C	0.9600
C5—H5	0.9300	C12—O2	1.425 (2)
C6—H6	0.9300	C12—H12A	0.9600
C7—C8	1.187 (2)	C12—H12B	0.9600
C8—H8	0.9300	C12—H12C	0.9600
C2—C1—C6	119.4 (2)	O1—C9—H9	109.2
C2—C1—C7	120.4 (1)	C11—C9—H9	109.2
C6—C1—C7	120.2 (1)	C10—C9—H9	109.2
O1—C2—C1	119.2 (1)	C9—C10—H10A	109.5
O1—C2—C3	120.8 (1)	C9—C10—H10B	109.5
C1—C2—C3	119.8 (1)	H10A—C10—H10B	109.5
O2—C3—C4	124.0 (1)	C9—C10—H10C	109.5
O2—C3—C2	116.3 (2)	H10A—C10—H10C	109.5
C4—C3—C2	119.8 (2)	H10B—C10—H10C	109.5
C3—C4—C5	120.0 (2)	C9—C11—H11A	109.5
C3—C4—H4	120.0	C9—C11—H11B	109.5
C5—C4—H4	120.0	H11A—C11—H11B	109.5
C6—C5—C4	120.8 (2)	C9—C11—H11C	109.5
C6—C5—H5	119.6	H11A—C11—H11C	109.5
C4—C5—H5	119.6	H11B—C11—H11C	109.5
C5—C6—C1	120.2 (2)	O2—C12—H12A	109.5
C5—C6—H6	119.9	O2—C12—H12B	109.5
C1—C6—H6	119.9	H12A—C12—H12B	109.5
C8—C7—C1	177.1 (2)	O2—C12—H12C	109.5
C7—C8—H8	180.0	H12A—C12—H12C	109.5
O1—C9—C11	105.1 (1)	H12B—C12—H12C	109.5
O1—C9—C10	110.4 (1)	C2—O1—C9	116.4 (1)
C11—C9—C10	113.5 (1)	C3—O2—C12	116.7 (1)
C6—C1—C2—O1	−175.17 (14)	C4—C5—C6—C1	1.6 (3)
C7—C1—C2—O1	5.0 (2)	C2—C1—C6—C5	−1.8 (2)
C6—C1—C2—C3	0.4 (2)	C7—C1—C6—C5	177.97 (16)
C7—C1—C2—C3	−179.40 (14)	C2—C1—C7—C8	−164 (3)
O1—C2—C3—O2	−2.3 (2)	C6—C1—C7—C8	16 (4)
C1—C2—C3—O2	−177.84 (14)	C1—C2—O1—C9	−113.00 (16)
O1—C2—C3—C4	176.78 (14)	C3—C2—O1—C9	71.46 (18)
C1—C2—C3—C4	1.3 (2)	C11—C9—O1—C2	−172.09 (13)
O2—C3—C4—C5	177.48 (16)	C10—C9—O1—C2	65.15 (17)
C2—C3—C4—C5	−1.6 (3)	C4—C3—O2—C12	3.2 (2)
C3—C4—C5—C6	0.1 (3)	C2—C3—O2—C12	−177.76 (14)