The title compounds, C
19H
19I
2NO
3 and C
19H
19Br
2NO
3, are derivatives of α-aminoisobutyric acid with halogen substituents at the
para and
meta positions, respectively. The ethoxycarbonyl and formamide side chains attached to the C
α atom of the molecule adopt extended and folded conformations, respectively. The crystal structures are stabilized by N—H
O, C—H
O, C—Br
O and C—I
O interactions.
Supporting information
CCDC references: 211752; 211753
Compound (I) was synthesized under phase-transfer conditions (PTC) using ethyl isocyanoacetate as a glycine equivalent (see Scheme 1) in a four-step sequence starting from p-toluidine (Kotha & Brahmachary, 1997; Kotha & Brahmachary, 2000). Thus, diazotization of compound (1) and subsequent iodination of the diazo derivative with KI gave 4-iodotoluene, (2). Benzylic bromination of (2) with NBS (please define) in the presence of AIBN/CCl4 reflux conditions gave (3). Alkylation of ethyl isocyanoacetate with (3) under PTC conditions gave the dialkylated product (4). Hydrolysis of the coupling product was achieved by treating (4) in HCl/diethyl ether/H2O solution at room temperature for a few hours to give the N-formyl derivative, (I). A similar procedure was used to synthesize compound (II).
The H atoms were fixed geometrically at calculated position.
For both compounds, data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1999); software used to prepare material for publication: SHELXL97.
(I) ethyl 2-formamido-2-(4-iodobenzyl)-3-(4-iodophenyl)propanoate
top
Crystal data top
C19H19I2NO3 | F(000) = 1080 |
Mr = 563.15 | Dx = 1.816 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 13.982 (7) Å | Cell parameters from 3103 reflections |
b = 8.922 (5) Å | θ = 2.3–26.2° |
c = 16.533 (8) Å | µ = 3.07 mm−1 |
β = 92.976 (8)° | T = 293 K |
V = 2059.8 (18) Å3 | Prism, colourless |
Z = 4 | 0.76 × 0.46 × 0.29 mm |
Data collection top
CCD Area Detector diffractometer | 4852 independent reflections |
Radiation source: fine-focus sealed tube | 4008 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.036 |
ω scans | θmax = 28.2°, θmin = 1.9° |
Absorption correction: multi-scan (SADABS; Bruker, 1999) | h = −18→18 |
Tmin = 0.203, Tmax = 0.472 | k = −11→11 |
32912 measured reflections | l = −21→21 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.056 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.160 | H-atom parameters constrained |
S = 1.01 | w = 1/[σ2(Fo2) + (0.0899P)2 + 2.926P] where P = (Fo2 + 2Fc2)/3 |
4852 reflections | (Δ/σ)max < 0.001 |
226 parameters | Δρmax = 1.47 e Å−3 |
0 restraints | Δρmin = −0.58 e Å−3 |
Crystal data top
C19H19I2NO3 | V = 2059.8 (18) Å3 |
Mr = 563.15 | Z = 4 |
Monoclinic, P21/n | Mo Kα radiation |
a = 13.982 (7) Å | µ = 3.07 mm−1 |
b = 8.922 (5) Å | T = 293 K |
c = 16.533 (8) Å | 0.76 × 0.46 × 0.29 mm |
β = 92.976 (8)° | |
Data collection top
CCD Area Detector diffractometer | 4852 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 1999) | 4008 reflections with I > 2σ(I) |
Tmin = 0.203, Tmax = 0.472 | Rint = 0.036 |
32912 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.056 | 0 restraints |
wR(F2) = 0.160 | H-atom parameters constrained |
S = 1.01 | Δρmax = 1.47 e Å−3 |
4852 reflections | Δρmin = −0.58 e Å−3 |
226 parameters | |
Special details top
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 (Å2) top | x | y | z | Uiso*/Ueq | |
I13 | −0.14253 (3) | 0.35627 (4) | 0.04848 (3) | 0.07422 (17) | |
I6 | 0.76573 (4) | 0.46913 (7) | −0.23825 (4) | 0.1169 (3) | |
O17 | 0.4014 (2) | 0.2510 (3) | 0.02073 (18) | 0.0522 (7) | |
O16 | 0.3415 (3) | 0.4393 (3) | −0.0552 (2) | 0.0590 (8) | |
O19 | 0.2259 (3) | 0.0578 (4) | −0.2465 (2) | 0.0745 (10) | |
N1 | 0.2725 (3) | 0.2609 (4) | −0.1717 (2) | 0.0460 (8) | |
H1 | 0.2705 | 0.3572 | −0.1705 | 0.055* | |
C10 | 0.1585 (3) | 0.1453 (5) | −0.0362 (3) | 0.0505 (10) | |
C1 | 0.3199 (3) | 0.1841 (4) | −0.1025 (2) | 0.0423 (8) | |
C2 | 0.4070 (3) | 0.0930 (4) | −0.1283 (3) | 0.0461 (9) | |
H2A | 0.4286 | 0.0295 | −0.0834 | 0.055* | |
H2B | 0.3861 | 0.0278 | −0.1727 | 0.055* | |
C3 | 0.4913 (3) | 0.1834 (4) | −0.1543 (2) | 0.0448 (8) | |
C16 | 0.3541 (3) | 0.3085 (4) | −0.0438 (2) | 0.0432 (8) | |
C9 | 0.2508 (3) | 0.0762 (5) | −0.0606 (3) | 0.0504 (9) | |
H9A | 0.2356 | −0.0066 | −0.0971 | 0.060* | |
H9B | 0.2840 | 0.0352 | −0.0126 | 0.060* | |
C15 | 0.1539 (3) | 0.2264 (6) | 0.0348 (3) | 0.0587 (11) | |
H15 | 0.2091 | 0.2387 | 0.0680 | 0.070* | |
C11 | 0.0739 (4) | 0.1295 (7) | −0.0841 (4) | 0.0714 (14) | |
H11 | 0.0752 | 0.0782 | −0.1330 | 0.086* | |
C14 | 0.0690 (4) | 0.2896 (6) | 0.0575 (3) | 0.0634 (12) | |
H14 | 0.0680 | 0.3469 | 0.1044 | 0.076* | |
C4 | 0.5750 (3) | 0.1886 (6) | −0.1072 (3) | 0.0613 (11) | |
H4 | 0.5792 | 0.1364 | −0.0584 | 0.074* | |
C19 | 0.2324 (4) | 0.1928 (6) | −0.2364 (3) | 0.0578 (11) | |
H19 | 0.2069 | 0.2538 | −0.2777 | 0.069* | |
C8 | 0.4884 (4) | 0.2638 (7) | −0.2263 (3) | 0.0655 (13) | |
H8 | 0.4328 | 0.2624 | −0.2597 | 0.079* | |
C12 | −0.0107 (4) | 0.1877 (8) | −0.0609 (4) | 0.0741 (15) | |
H12 | −0.0664 | 0.1736 | −0.0932 | 0.089* | |
C13 | −0.0138 (3) | 0.2675 (5) | 0.0107 (3) | 0.0557 (10) | |
C6 | 0.6486 (4) | 0.3465 (5) | −0.2010 (3) | 0.0632 (13) | |
C17 | 0.4373 (5) | 0.3587 (6) | 0.0815 (3) | 0.0761 (16) | |
H17A | 0.4766 | 0.4329 | 0.0562 | 0.091* | |
H17B | 0.3837 | 0.4102 | 0.1043 | 0.091* | |
C7 | 0.5658 (5) | 0.3453 (6) | −0.2494 (4) | 0.0718 (14) | |
H7 | 0.5621 | 0.3993 | −0.2975 | 0.086* | |
C5 | 0.6534 (4) | 0.2697 (7) | −0.1306 (4) | 0.0725 (14) | |
H5 | 0.7094 | 0.2712 | −0.0977 | 0.087* | |
C18 | 0.4924 (8) | 0.2847 (8) | 0.1447 (5) | 0.128 (4) | |
H18A | 0.5161 | 0.3572 | 0.1837 | 0.192* | |
H18B | 0.5454 | 0.2339 | 0.1221 | 0.192* | |
H18C | 0.4529 | 0.2132 | 0.1707 | 0.192* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
I13 | 0.0552 (2) | 0.0728 (3) | 0.0959 (3) | 0.00482 (15) | 0.01487 (18) | 0.00889 (18) |
I6 | 0.1045 (4) | 0.1038 (4) | 0.1479 (5) | −0.0480 (3) | 0.0587 (3) | −0.0310 (3) |
O17 | 0.0611 (18) | 0.0434 (15) | 0.0512 (16) | 0.0017 (13) | −0.0065 (14) | −0.0052 (12) |
O16 | 0.075 (2) | 0.0330 (14) | 0.0683 (19) | 0.0016 (14) | −0.0061 (16) | −0.0049 (13) |
O19 | 0.091 (3) | 0.056 (2) | 0.074 (2) | −0.0096 (19) | −0.016 (2) | −0.0140 (17) |
N1 | 0.0497 (18) | 0.0317 (15) | 0.0557 (19) | 0.0002 (13) | −0.0046 (15) | 0.0015 (14) |
C10 | 0.048 (2) | 0.046 (2) | 0.058 (2) | −0.0104 (17) | −0.0014 (19) | 0.0101 (18) |
C1 | 0.0422 (19) | 0.0308 (16) | 0.054 (2) | −0.0020 (15) | 0.0001 (16) | −0.0001 (16) |
C2 | 0.047 (2) | 0.0322 (17) | 0.059 (2) | 0.0031 (16) | −0.0004 (18) | −0.0025 (16) |
C3 | 0.051 (2) | 0.0371 (18) | 0.047 (2) | 0.0041 (16) | 0.0052 (17) | −0.0084 (16) |
C16 | 0.0409 (19) | 0.0393 (19) | 0.049 (2) | 0.0000 (15) | 0.0016 (16) | −0.0029 (16) |
C9 | 0.048 (2) | 0.0362 (19) | 0.067 (3) | −0.0017 (16) | 0.0030 (19) | 0.0049 (18) |
C15 | 0.048 (2) | 0.074 (3) | 0.054 (2) | −0.007 (2) | −0.0027 (19) | 0.001 (2) |
C11 | 0.054 (3) | 0.086 (4) | 0.073 (3) | −0.007 (3) | −0.003 (2) | −0.025 (3) |
C14 | 0.057 (3) | 0.074 (3) | 0.059 (3) | −0.010 (2) | 0.009 (2) | −0.010 (2) |
C4 | 0.048 (2) | 0.075 (3) | 0.061 (3) | 0.006 (2) | −0.001 (2) | 0.007 (2) |
C19 | 0.061 (3) | 0.054 (3) | 0.057 (3) | −0.002 (2) | −0.011 (2) | 0.000 (2) |
C8 | 0.059 (3) | 0.084 (4) | 0.052 (3) | 0.000 (3) | 0.001 (2) | 0.002 (2) |
C12 | 0.045 (3) | 0.096 (4) | 0.080 (3) | −0.003 (3) | −0.008 (2) | −0.009 (3) |
C13 | 0.048 (2) | 0.054 (2) | 0.066 (3) | −0.0077 (19) | 0.008 (2) | 0.011 (2) |
C6 | 0.059 (3) | 0.055 (3) | 0.077 (3) | −0.004 (2) | 0.021 (2) | −0.017 (2) |
C17 | 0.101 (4) | 0.059 (3) | 0.066 (3) | −0.001 (3) | −0.019 (3) | −0.015 (2) |
C7 | 0.080 (4) | 0.069 (3) | 0.069 (3) | 0.000 (3) | 0.019 (3) | 0.010 (2) |
C5 | 0.049 (3) | 0.091 (4) | 0.078 (3) | −0.005 (3) | 0.003 (2) | −0.007 (3) |
C18 | 0.179 (9) | 0.074 (4) | 0.121 (6) | 0.033 (5) | −0.080 (7) | −0.030 (4) |
Geometric parameters (Å, º) top
I13—C13 | 2.091 (5) | C15—H15 | 0.9300 |
I6—C6 | 2.089 (5) | C11—C12 | 1.365 (8) |
O17—C16 | 1.329 (5) | C11—H11 | 0.9300 |
O17—C17 | 1.460 (6) | C14—C13 | 1.373 (7) |
O16—C16 | 1.194 (5) | C14—H14 | 0.9300 |
O19—C19 | 1.219 (6) | C4—C5 | 1.385 (8) |
N1—C19 | 1.329 (6) | C4—H4 | 0.9300 |
N1—C1 | 1.463 (5) | C19—H19 | 0.9300 |
N1—H1 | 0.8600 | C8—C7 | 1.374 (8) |
C10—C15 | 1.383 (7) | C8—H8 | 0.9300 |
C10—C11 | 1.396 (7) | C12—C13 | 1.384 (8) |
C10—C9 | 1.504 (6) | C12—H12 | 0.9300 |
C1—C16 | 1.534 (5) | C6—C5 | 1.349 (8) |
C1—C2 | 1.543 (5) | C6—C7 | 1.373 (8) |
C1—C9 | 1.552 (6) | C17—C18 | 1.427 (9) |
C2—C3 | 1.509 (6) | C17—H17A | 0.9700 |
C2—H2A | 0.9700 | C17—H17B | 0.9700 |
C2—H2B | 0.9700 | C7—H7 | 0.9300 |
C3—C4 | 1.373 (6) | C5—H5 | 0.9300 |
C3—C8 | 1.389 (7) | C18—H18A | 0.9600 |
C9—H9A | 0.9700 | C18—H18B | 0.9600 |
C9—H9B | 0.9700 | C18—H18C | 0.9600 |
C15—C14 | 1.384 (7) | | |
| | | |
C16—O17—C17 | 115.9 (4) | C13—C14—H14 | 120.0 |
C19—N1—C1 | 124.8 (4) | C15—C14—H14 | 120.0 |
C19—N1—H1 | 117.6 | C3—C4—C5 | 121.5 (5) |
C1—N1—H1 | 117.6 | C3—C4—H4 | 119.2 |
C15—C10—C11 | 117.3 (5) | C5—C4—H4 | 119.2 |
C15—C10—C9 | 121.3 (4) | O19—C19—N1 | 126.0 (5) |
C11—C10—C9 | 121.4 (4) | O19—C19—H19 | 117.0 |
N1—C1—C16 | 105.6 (3) | N1—C19—H19 | 117.0 |
N1—C1—C2 | 111.2 (3) | C7—C8—C3 | 121.5 (5) |
C16—C1—C2 | 109.4 (3) | C7—C8—H8 | 119.3 |
N1—C1—C9 | 111.8 (3) | C3—C8—H8 | 119.3 |
C16—C1—C9 | 110.4 (3) | C13—C12—C11 | 120.2 (5) |
C2—C1—C9 | 108.4 (3) | C13—C12—H12 | 119.9 |
C3—C2—C1 | 115.9 (3) | C11—C12—H12 | 119.9 |
C3—C2—H2A | 108.3 | C14—C13—C12 | 119.5 (5) |
C1—C2—H2A | 108.3 | C14—C13—I13 | 119.4 (4) |
C3—C2—H2B | 108.3 | C12—C13—I13 | 121.1 (4) |
C1—C2—H2B | 108.3 | C5—C6—C7 | 120.1 (5) |
H2A—C2—H2B | 107.4 | C5—C6—I6 | 121.1 (4) |
C4—C3—C8 | 117.1 (4) | C7—C6—I6 | 118.9 (4) |
C4—C3—C2 | 120.8 (4) | C18—C17—O17 | 110.6 (5) |
C8—C3—C2 | 122.1 (4) | C18—C17—H17A | 109.5 |
O16—C16—O17 | 124.5 (4) | O17—C17—H17A | 109.5 |
O16—C16—C1 | 124.7 (4) | C18—C17—H17B | 109.5 |
O17—C16—C1 | 110.8 (3) | O17—C17—H17B | 109.5 |
C10—C9—C1 | 115.4 (3) | H17A—C17—H17B | 108.1 |
C10—C9—H9A | 108.4 | C8—C7—C6 | 119.7 (5) |
C1—C9—H9A | 108.4 | C8—C7—H7 | 120.2 |
C10—C9—H9B | 108.4 | C6—C7—H7 | 120.2 |
C1—C9—H9B | 108.4 | C6—C5—C4 | 120.1 (5) |
H9A—C9—H9B | 107.5 | C6—C5—H5 | 119.9 |
C10—C15—C14 | 121.4 (4) | C4—C5—H5 | 119.9 |
C10—C15—H15 | 119.3 | C17—C18—H18A | 109.5 |
C14—C15—H15 | 119.3 | C17—C18—H18B | 109.5 |
C12—C11—C10 | 121.6 (5) | H18A—C18—H18B | 109.5 |
C12—C11—H11 | 119.2 | C17—C18—H18C | 109.5 |
C10—C11—H11 | 119.2 | H18A—C18—H18C | 109.5 |
C13—C14—C15 | 119.9 (5) | H18B—C18—H18C | 109.5 |
| | | |
C19—N1—C1—C16 | −179.8 (4) | C9—C10—C15—C14 | −179.8 (4) |
C19—N1—C1—C2 | 61.6 (5) | C15—C10—C11—C12 | −2.0 (9) |
C19—N1—C1—C9 | −59.7 (5) | C9—C10—C11—C12 | 177.7 (5) |
N1—C1—C2—C3 | 68.8 (4) | C10—C15—C14—C13 | 2.5 (8) |
C16—C1—C2—C3 | −47.5 (5) | C8—C3—C4—C5 | −0.3 (7) |
C9—C1—C2—C3 | −167.8 (4) | C2—C3—C4—C5 | 179.3 (5) |
C1—C2—C3—C4 | 109.9 (5) | C1—N1—C19—O19 | 2.8 (8) |
C1—C2—C3—C8 | −70.4 (5) | C4—C3—C8—C7 | −0.2 (8) |
C17—O17—C16—O16 | 1.6 (7) | C2—C3—C8—C7 | −179.8 (5) |
C17—O17—C16—C1 | −179.6 (4) | C10—C11—C12—C13 | 1.5 (10) |
N1—C1—C16—O16 | 0.8 (6) | C15—C14—C13—C12 | −2.9 (8) |
C2—C1—C16—O16 | 120.6 (5) | C15—C14—C13—I13 | 177.5 (4) |
C9—C1—C16—O16 | −120.3 (5) | C11—C12—C13—C14 | 1.0 (9) |
N1—C1—C16—O17 | −177.9 (3) | C11—C12—C13—I13 | −179.4 (5) |
C2—C1—C16—O17 | −58.1 (4) | C16—O17—C17—C18 | −175.8 (7) |
C9—C1—C16—O17 | 61.0 (4) | C3—C8—C7—C6 | 0.8 (8) |
C15—C10—C9—C1 | −81.7 (5) | C5—C6—C7—C8 | −0.9 (8) |
C11—C10—C9—C1 | 98.6 (5) | I6—C6—C7—C8 | 179.2 (4) |
N1—C1—C9—C10 | −53.3 (5) | C7—C6—C5—C4 | 0.4 (8) |
C16—C1—C9—C10 | 64.0 (5) | I6—C6—C5—C4 | −179.7 (4) |
C2—C1—C9—C10 | −176.2 (4) | C3—C4—C5—C6 | 0.2 (9) |
C11—C10—C15—C14 | −0.1 (7) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O19i | 0.86 | 2.26 | 2.975 (5) | 141 |
C9—H9A···O19 | 0.97 | 2.53 | 3.080 (6) | 116 |
C9—H9B···O17 | 0.97 | 2.57 | 2.896 (5) | 100 |
C2—H2B···O19 | 0.97 | 2.51 | 3.133 (6) | 122 |
N1—H1···O16 | 0.86 | 2.23 | 2.643 (5) | 110 |
Symmetry code: (i) −x+1/2, y+1/2, −z−1/2. |
(II) ethyl 2-formamido-2-(3-bromobenzyl)-3-(3-bromophenyl)propanoate
top
Crystal data top
C19H19Br2NO3 | F(000) = 936 |
Mr = 469.17 | Dx = 1.569 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 11.380 (3) Å | Cell parameters from 4648 reflections |
b = 14.867 (3) Å | θ = 2.1–29.8° |
c = 12.525 (3) Å | µ = 4.10 mm−1 |
β = 110.431 (4)° | T = 293 K |
V = 1985.8 (7) Å3 | Irregular, colorless |
Z = 4 | 0.43 × 0.25 × 0.18 mm |
Data collection top
Bruker CCD area-detector diffractometer | 4648 independent reflections |
Radiation source: fine-focus sealed tube | 2163 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.092 |
ϕ and ω scans | θmax = 28.0°, θmin = 2.1° |
Absorption correction: multi-scan (SADABS; Bruker, 1999) | h = −14→14 |
Tmin = 0.272, Tmax = 0.526 | k = −19→19 |
17080 measured reflections | l = −14→16 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.051 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.147 | H-atom parameters constrained |
S = 0.88 | w = 1/[σ2(Fo2) + (0.0772P)2] where P = (Fo2 + 2Fc2)/3 |
4648 reflections | (Δ/σ)max = 0.001 |
242 parameters | Δρmax = 1.14 e Å−3 |
111 restraints | Δρmin = −0.74 e Å−3 |
Crystal data top
C19H19Br2NO3 | V = 1985.8 (7) Å3 |
Mr = 469.17 | Z = 4 |
Monoclinic, P21/n | Mo Kα radiation |
a = 11.380 (3) Å | µ = 4.10 mm−1 |
b = 14.867 (3) Å | T = 293 K |
c = 12.525 (3) Å | 0.43 × 0.25 × 0.18 mm |
β = 110.431 (4)° | |
Data collection top
Bruker CCD area-detector diffractometer | 4648 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 1999) | 2163 reflections with I > 2σ(I) |
Tmin = 0.272, Tmax = 0.526 | Rint = 0.092 |
17080 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.051 | 111 restraints |
wR(F2) = 0.147 | H-atom parameters constrained |
S = 0.88 | Δρmax = 1.14 e Å−3 |
4648 reflections | Δρmin = −0.74 e Å−3 |
242 parameters | |
Special details top
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 (Å2) top | x | y | z | Uiso*/Ueq | Occ. (<1) |
Br7 | 0.94125 (5) | 0.08506 (3) | 0.15153 (4) | 0.0729 (2) | |
Br12 | 0.75848 (8) | 0.87262 (5) | −0.05108 (7) | 0.1237 (3) | |
O19 | 0.5956 (3) | 0.5488 (2) | −0.1695 (3) | 0.0736 (9) | |
C1 | 0.7637 (3) | 0.4759 (3) | 0.0458 (3) | 0.0452 (9) | |
C7 | 0.8655 (4) | 0.1728 (3) | 0.0379 (4) | 0.0537 (10) | |
O17 | 0.8801 (3) | 0.4208 (2) | 0.2294 (3) | 0.0769 (10) | |
N1 | 0.7910 (3) | 0.5094 (2) | −0.0518 (3) | 0.0482 (8) | |
H1 | 0.8681 | 0.5092 | −0.0474 | 0.058* | |
C2 | 0.6827 (4) | 0.3892 (3) | 0.0132 (4) | 0.0522 (10) | |
H2A | 0.6564 | 0.3726 | 0.0763 | 0.063* | |
H2B | 0.6079 | 0.4022 | −0.0517 | 0.063* | |
C15 | 0.8427 (4) | 0.6540 (4) | 0.2301 (4) | 0.0709 (13) | |
H15 | 0.8611 | 0.6102 | 0.2866 | 0.085* | |
C8 | 0.8061 (4) | 0.2448 (3) | 0.0656 (4) | 0.0550 (11) | |
H8 | 0.8037 | 0.2499 | 0.1389 | 0.066* | |
O16 | 0.9890 (3) | 0.4640 (3) | 0.1224 (3) | 0.0779 (10) | |
C19 | 0.7064 (5) | 0.5406 (3) | −0.1477 (4) | 0.0570 (11) | |
H19 | 0.7369 | 0.5581 | −0.2045 | 0.068* | |
C3 | 0.7493 (4) | 0.3100 (3) | −0.0158 (4) | 0.0531 (10) | |
C11 | 0.7327 (4) | 0.7018 (3) | 0.0406 (4) | 0.0670 (12) | |
H11 | 0.6758 | 0.6914 | −0.0323 | 0.080* | |
C9 | 0.6931 (4) | 0.5455 (3) | 0.0941 (4) | 0.0592 (11) | |
H9A | 0.6096 | 0.5541 | 0.0388 | 0.071* | |
H9B | 0.6843 | 0.5209 | 0.1626 | 0.071* | |
C16 | 0.8914 (4) | 0.4540 (3) | 0.1353 (4) | 0.0553 (11) | |
C6 | 0.8729 (4) | 0.1630 (3) | −0.0687 (4) | 0.0646 (12) | |
H6 | 0.9144 | 0.1145 | −0.0863 | 0.078* | |
C13 | 0.8757 (5) | 0.8022 (4) | 0.1734 (5) | 0.0825 (15) | |
H13 | 0.9142 | 0.8582 | 0.1901 | 0.099* | |
C5 | 0.8163 (5) | 0.2280 (3) | −0.1482 (4) | 0.0705 (13) | |
H5 | 0.8200 | 0.2231 | −0.2210 | 0.085* | |
C10 | 0.7570 (4) | 0.6357 (3) | 0.1220 (4) | 0.0576 (11) | |
C4 | 0.7550 (4) | 0.2995 (3) | −0.1235 (4) | 0.0615 (11) | |
H4 | 0.7167 | 0.3416 | −0.1798 | 0.074* | |
C14 | 0.9001 (5) | 0.7369 (4) | 0.2537 (5) | 0.0861 (16) | |
H14 | 0.9570 | 0.7482 | 0.3264 | 0.103* | |
C12 | 0.7924 (5) | 0.7831 (3) | 0.0667 (5) | 0.0757 (13) | |
C17A | 1.0048 (11) | 0.4083 (12) | 0.3147 (10) | 0.108 (6) | 0.579 (15) |
H17A | 1.0587 | 0.3758 | 0.2828 | 0.130* | 0.579 (15) |
H17B | 1.0431 | 0.4658 | 0.3434 | 0.130* | 0.579 (15) |
C18A | 0.9827 (11) | 0.3543 (9) | 0.4084 (9) | 0.142 (7) | 0.579 (15) |
H18A | 1.0607 | 0.3464 | 0.4702 | 0.213* | 0.579 (15) |
H18B | 0.9487 | 0.2966 | 0.3792 | 0.213* | 0.579 (15) |
H18C | 0.9247 | 0.3858 | 0.4352 | 0.213* | 0.579 (15) |
C17B | 0.9741 (11) | 0.3658 (9) | 0.3089 (9) | 0.094 (6) | 0.421 (15) |
H17C | 1.0417 | 0.3515 | 0.2814 | 0.113* | 0.421 (15) |
H17D | 0.9389 | 0.3105 | 0.3259 | 0.113* | 0.421 (15) |
C18B | 1.017 (2) | 0.4279 (16) | 0.4110 (16) | 0.165 (11) | 0.421 (15) |
H18D | 1.0839 | 0.3997 | 0.4714 | 0.247* | 0.421 (15) |
H18E | 0.9486 | 0.4402 | 0.4363 | 0.247* | 0.421 (15) |
H18F | 1.0472 | 0.4832 | 0.3901 | 0.247* | 0.421 (15) |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Br7 | 0.0846 (4) | 0.0531 (3) | 0.0735 (4) | 0.0107 (2) | 0.0183 (3) | 0.0122 (2) |
Br12 | 0.1617 (7) | 0.0705 (4) | 0.1280 (7) | −0.0252 (4) | 0.0368 (5) | −0.0021 (4) |
O19 | 0.061 (2) | 0.068 (2) | 0.072 (2) | 0.0116 (17) | −0.0020 (17) | 0.0005 (17) |
C1 | 0.041 (2) | 0.052 (2) | 0.045 (2) | 0.0084 (17) | 0.0192 (19) | 0.0048 (18) |
C7 | 0.053 (3) | 0.044 (2) | 0.061 (3) | 0.0017 (19) | 0.015 (2) | 0.003 (2) |
O17 | 0.074 (2) | 0.111 (3) | 0.0454 (19) | 0.0215 (19) | 0.0212 (16) | 0.0185 (18) |
N1 | 0.0451 (19) | 0.053 (2) | 0.046 (2) | 0.0026 (15) | 0.0156 (16) | 0.0055 (16) |
C2 | 0.050 (2) | 0.051 (2) | 0.059 (3) | 0.0039 (18) | 0.024 (2) | 0.010 (2) |
C15 | 0.063 (3) | 0.088 (3) | 0.062 (3) | 0.003 (3) | 0.022 (2) | −0.021 (3) |
C8 | 0.062 (3) | 0.051 (2) | 0.056 (3) | 0.002 (2) | 0.025 (2) | 0.004 (2) |
O16 | 0.0458 (18) | 0.122 (3) | 0.063 (2) | 0.0101 (18) | 0.0159 (16) | 0.018 (2) |
C19 | 0.068 (3) | 0.050 (2) | 0.045 (3) | 0.004 (2) | 0.010 (2) | 0.002 (2) |
C3 | 0.052 (2) | 0.045 (2) | 0.062 (3) | −0.0005 (18) | 0.019 (2) | 0.004 (2) |
C11 | 0.059 (3) | 0.058 (3) | 0.073 (3) | −0.004 (2) | 0.009 (2) | −0.019 (2) |
C9 | 0.050 (2) | 0.060 (2) | 0.069 (3) | 0.005 (2) | 0.023 (2) | −0.008 (2) |
C16 | 0.057 (3) | 0.064 (3) | 0.044 (3) | 0.006 (2) | 0.018 (2) | 0.005 (2) |
C6 | 0.074 (3) | 0.057 (3) | 0.065 (3) | 0.010 (2) | 0.028 (3) | −0.006 (2) |
C13 | 0.075 (3) | 0.082 (4) | 0.096 (4) | −0.023 (3) | 0.036 (3) | −0.045 (3) |
C5 | 0.094 (4) | 0.067 (3) | 0.053 (3) | 0.010 (3) | 0.029 (3) | −0.001 (2) |
C10 | 0.047 (2) | 0.061 (3) | 0.067 (3) | 0.000 (2) | 0.021 (2) | −0.019 (2) |
C4 | 0.072 (3) | 0.051 (2) | 0.057 (3) | 0.008 (2) | 0.017 (2) | 0.006 (2) |
C14 | 0.071 (3) | 0.114 (5) | 0.067 (4) | −0.013 (3) | 0.016 (3) | −0.043 (3) |
C12 | 0.076 (3) | 0.063 (3) | 0.089 (4) | −0.009 (3) | 0.030 (3) | −0.019 (3) |
C17A | 0.063 (6) | 0.174 (17) | 0.067 (8) | −0.006 (9) | −0.003 (5) | 0.034 (9) |
C18A | 0.112 (10) | 0.188 (17) | 0.112 (12) | 0.032 (11) | 0.020 (8) | 0.081 (12) |
C17B | 0.097 (13) | 0.126 (15) | 0.063 (9) | 0.012 (10) | 0.032 (8) | 0.042 (7) |
C18B | 0.149 (19) | 0.16 (2) | 0.115 (15) | 0.026 (17) | −0.041 (14) | −0.008 (15) |
Geometric parameters (Å, º) top
Br7—C7 | 1.901 (4) | C11—C10 | 1.373 (6) |
Br12—C12 | 1.923 (6) | C11—H11 | 0.9300 |
O19—C19 | 1.200 (5) | C9—C10 | 1.507 (6) |
C1—N1 | 1.450 (5) | C9—H9A | 0.9700 |
C1—C16 | 1.529 (6) | C9—H9B | 0.9700 |
C1—C2 | 1.554 (5) | C6—C5 | 1.376 (6) |
C1—C9 | 1.555 (5) | C6—H6 | 0.9300 |
C7—C8 | 1.373 (5) | C13—C14 | 1.355 (8) |
C7—C6 | 1.375 (6) | C13—C12 | 1.371 (7) |
O17—C16 | 1.325 (5) | C13—H13 | 0.9300 |
O17—C17B | 1.436 (11) | C5—C4 | 1.365 (6) |
O17—C17A | 1.460 (11) | C5—H5 | 0.9300 |
N1—C19 | 1.334 (5) | C4—H4 | 0.9300 |
N1—H1 | 0.8600 | C14—H14 | 0.9300 |
C2—C3 | 1.510 (6) | C17A—C18A | 1.513 (15) |
C2—H2A | 0.9700 | C17A—H17A | 0.9700 |
C2—H2B | 0.9700 | C17A—H17B | 0.9700 |
C15—C14 | 1.378 (7) | C18A—H18A | 0.9600 |
C15—C10 | 1.392 (6) | C18A—H18B | 0.9600 |
C15—H15 | 0.9300 | C18A—H18C | 0.9600 |
C8—C3 | 1.392 (6) | C17B—C18B | 1.513 (17) |
C8—H8 | 0.9300 | C17B—H17C | 0.9700 |
O16—C16 | 1.186 (5) | C17B—H17D | 0.9700 |
C19—H19 | 0.9300 | C18B—H18D | 0.9600 |
C3—C4 | 1.383 (6) | C18B—H18E | 0.9600 |
C11—C12 | 1.369 (6) | C18B—H18F | 0.9600 |
| | | |
N1—C1—C16 | 105.2 (3) | C7—C6—C5 | 117.1 (4) |
N1—C1—C2 | 110.2 (3) | C7—C6—H6 | 121.4 |
C16—C1—C2 | 109.9 (3) | C5—C6—H6 | 121.4 |
N1—C1—C9 | 113.0 (3) | C14—C13—C12 | 118.0 (5) |
C16—C1—C9 | 110.1 (3) | C14—C13—H13 | 121.0 |
C2—C1—C9 | 108.3 (3) | C12—C13—H13 | 121.0 |
C8—C7—C6 | 122.1 (4) | C4—C5—C6 | 122.0 (4) |
C8—C7—Br7 | 118.7 (3) | C4—C5—H5 | 119.0 |
C6—C7—Br7 | 119.2 (3) | C6—C5—H5 | 119.0 |
C16—O17—C17B | 123.3 (6) | C11—C10—C15 | 118.3 (4) |
C16—O17—C17A | 109.1 (6) | C11—C10—C9 | 120.6 (4) |
C17B—O17—C17A | 28.5 (9) | C15—C10—C9 | 121.1 (5) |
C19—N1—C1 | 125.4 (4) | C5—C4—C3 | 120.7 (4) |
C19—N1—H1 | 117.3 | C5—C4—H4 | 119.6 |
C1—N1—H1 | 117.3 | C3—C4—H4 | 119.6 |
C3—C2—C1 | 114.1 (3) | C13—C14—C15 | 121.5 (5) |
C3—C2—H2A | 108.7 | C13—C14—H14 | 119.3 |
C1—C2—H2A | 108.7 | C15—C14—H14 | 119.3 |
C3—C2—H2B | 108.7 | C11—C12—C13 | 122.1 (5) |
C1—C2—H2B | 108.7 | C11—C12—Br12 | 118.5 (4) |
H2A—C2—H2B | 107.6 | C13—C12—Br12 | 119.4 (4) |
C14—C15—C10 | 120.1 (5) | C18A—C17A—O17 | 104.7 (10) |
C14—C15—H15 | 119.9 | C18A—C17A—H17A | 110.8 |
C10—C15—H15 | 119.9 | O17—C17A—H17A | 110.8 |
C7—C8—C3 | 120.1 (4) | C18A—C17A—H17B | 110.8 |
C7—C8—H8 | 120.0 | O17—C17A—H17B | 110.8 |
C3—C8—H8 | 120.0 | H17A—C17A—H17B | 108.9 |
O19—C19—N1 | 127.7 (4) | C17A—C18A—H18A | 109.5 |
O19—C19—H19 | 116.2 | C17A—C18A—H18B | 109.5 |
N1—C19—H19 | 116.2 | H18A—C18A—H18B | 109.5 |
C4—C3—C8 | 117.9 (4) | C17A—C18A—H18C | 109.5 |
C4—C3—C2 | 121.4 (4) | H18A—C18A—H18C | 109.5 |
C8—C3—C2 | 120.7 (4) | H18B—C18A—H18C | 109.5 |
C12—C11—C10 | 120.0 (4) | O17—C17B—C18B | 100.5 (11) |
C12—C11—H11 | 120.0 | O17—C17B—H17C | 111.7 |
C10—C11—H11 | 120.0 | C18B—C17B—H17C | 111.7 |
C10—C9—C1 | 114.1 (3) | O17—C17B—H17D | 111.7 |
C10—C9—H9A | 108.7 | C18B—C17B—H17D | 111.7 |
C1—C9—H9A | 108.7 | H17C—C17B—H17D | 109.4 |
C10—C9—H9B | 108.7 | C17B—C18B—H18D | 109.5 |
C1—C9—H9B | 108.7 | C17B—C18B—H18E | 109.5 |
H9A—C9—H9B | 107.6 | H18D—C18B—H18E | 109.5 |
O16—C16—O17 | 123.6 (4) | C17B—C18B—H18F | 109.5 |
O16—C16—C1 | 124.7 (4) | H18D—C18B—H18F | 109.5 |
O17—C16—C1 | 111.6 (4) | H18E—C18B—H18F | 109.5 |
| | | |
C16—C1—N1—C19 | −176.6 (4) | C2—C1—C16—O17 | −60.2 (4) |
C2—C1—N1—C19 | 65.0 (5) | C9—C1—C16—O17 | 59.1 (5) |
C9—C1—N1—C19 | −56.4 (5) | C8—C7—C6—C5 | −0.9 (7) |
N1—C1—C2—C3 | 66.0 (4) | Br7—C7—C6—C5 | 179.8 (3) |
C16—C1—C2—C3 | −49.6 (5) | C7—C6—C5—C4 | −0.1 (7) |
C9—C1—C2—C3 | −169.9 (4) | C12—C11—C10—C15 | 0.2 (6) |
C6—C7—C8—C3 | 0.9 (6) | C12—C11—C10—C9 | −179.3 (4) |
Br7—C7—C8—C3 | −179.8 (3) | C14—C15—C10—C11 | 0.4 (7) |
C1—N1—C19—O19 | 2.1 (7) | C14—C15—C10—C9 | 179.9 (4) |
C7—C8—C3—C4 | 0.1 (6) | C1—C9—C10—C11 | 88.3 (5) |
C7—C8—C3—C2 | 179.6 (4) | C1—C9—C10—C15 | −91.2 (5) |
C1—C2—C3—C4 | −83.5 (5) | C6—C5—C4—C3 | 1.1 (7) |
C1—C2—C3—C8 | 97.1 (4) | C8—C3—C4—C5 | −1.0 (6) |
N1—C1—C9—C10 | −53.6 (5) | C2—C3—C4—C5 | 179.5 (4) |
C16—C1—C9—C10 | 63.7 (5) | C12—C13—C14—C15 | −0.6 (8) |
C2—C1—C9—C10 | −176.0 (4) | C10—C15—C14—C13 | −0.2 (8) |
C17B—O17—C16—O16 | −22.0 (9) | C10—C11—C12—C13 | −1.0 (7) |
C17A—O17—C16—O16 | 5.7 (10) | C10—C11—C12—Br12 | 178.5 (3) |
C17B—O17—C16—C1 | 157.0 (7) | C14—C13—C12—C11 | 1.2 (8) |
C17A—O17—C16—C1 | −175.3 (8) | C14—C13—C12—Br12 | −178.2 (4) |
N1—C1—C16—O16 | 0.1 (6) | C16—O17—C17A—C18A | −169.4 (11) |
C2—C1—C16—O16 | 118.7 (5) | C17B—O17—C17A—C18A | −43.9 (9) |
C9—C1—C16—O16 | −122.0 (5) | C16—O17—C17B—C18B | 112.9 (15) |
N1—C1—C16—O17 | −178.9 (3) | C17A—O17—C17B—C18B | 45.9 (17) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O16 | 0.86 | 2.20 | 2.620 (4) | 110 |
C2—H2B···O19 | 0.97 | 2.61 | 3.205 (5) | 120 |
C9—H9A···O19 | 0.97 | 2.56 | 3.095 (6) | 115 |
N1—H1···O16i | 0.86 | 2.18 | 2.959 (5) | 150 |
Symmetry code: (i) −x+2, −y+1, −z. |
Experimental details
| (I) | (II) |
Crystal data |
Chemical formula | C19H19I2NO3 | C19H19Br2NO3 |
Mr | 563.15 | 469.17 |
Crystal system, space group | Monoclinic, P21/n | Monoclinic, P21/n |
Temperature (K) | 293 | 293 |
a, b, c (Å) | 13.982 (7), 8.922 (5), 16.533 (8) | 11.380 (3), 14.867 (3), 12.525 (3) |
β (°) | 92.976 (8) | 110.431 (4) |
V (Å3) | 2059.8 (18) | 1985.8 (7) |
Z | 4 | 4 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 3.07 | 4.10 |
Crystal size (mm) | 0.76 × 0.46 × 0.29 | 0.43 × 0.25 × 0.18 |
|
Data collection |
Diffractometer | CCD Area Detector diffractometer | Bruker CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 1999) | Multi-scan (SADABS; Bruker, 1999) |
Tmin, Tmax | 0.203, 0.472 | 0.272, 0.526 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 32912, 4852, 4008 | 17080, 4648, 2163 |
Rint | 0.036 | 0.092 |
(sin θ/λ)max (Å−1) | 0.665 | 0.660 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.056, 0.160, 1.01 | 0.051, 0.147, 0.88 |
No. of reflections | 4852 | 4648 |
No. of parameters | 226 | 242 |
No. of restraints | 0 | 111 |
H-atom treatment | H-atom parameters constrained | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 1.47, −0.58 | 1.14, −0.74 |
Hydrogen-bond geometry (Å, º) for (I) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O19i | 0.86 | 2.26 | 2.975 (5) | 141 |
C9—H9A···O19 | 0.97 | 2.53 | 3.080 (6) | 116 |
C9—H9B···O17 | 0.97 | 2.57 | 2.896 (5) | 100 |
C2—H2B···O19 | 0.97 | 2.51 | 3.133 (6) | 122 |
N1—H1···O16 | 0.86 | 2.23 | 2.643 (5) | 110 |
Symmetry code: (i) −x+1/2, y+1/2, −z−1/2. |
Hydrogen-bond geometry (Å, º) for (II) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O16 | 0.86 | 2.20 | 2.620 (4) | 110 |
C2—H2B···O19 | 0.97 | 2.61 | 3.205 (5) | 120 |
C9—H9A···O19 | 0.97 | 2.56 | 3.095 (6) | 115 |
N1—H1···O16i | 0.86 | 2.18 | 2.959 (5) | 150 |
Symmetry code: (i) −x+2, −y+1, −z. |
Recently, there has been an increasing interest in the synthesis of structural variations of α-aminoisobutyric acid (Aib) with the aim of incorporating them into peptides (Karle et al., 1994; Ramesh & Balaram, 1999; Formaggio et al., 2000). Dibenzylglycine (Dbzg) is a special structural variant of Aib (Kotha et al., 2002; Scott et al., 1997). The presence of two benzyl groups at α position of Dbzg not only provides rigidity to the peptide backbone, but also acts as a useful vehicle for studying π–π interaction (Studer & Seebach, 1995; Damodharan, Shamaladevi et al., 2002). In this paper, we present the crystal structures of two derivatives of Dbzg with iodine- and bromine-substituted at para and meta position of the benzene rings, namely ethyl 2-formamido-2-(4-iodobenzyl)-3-(4-iodophenyl)propanoate, (I), and ethyl 2-formamido-2-(3-bromobenzyl)-3-(3-bromophenyl)propanoate, (II).
Compound (I) crystallizes from acetone–dichloromethane (1:1), while compound (II) crystallizes from n-propanol–dichloromethane (1:3) both in the P21/n space group (Fig. 1). The I and Br atoms are coplanar with their respective benzene rings. The N-formyl and ethyl ester side chains adopt folded and extended conformations in both compounds [C1—N1—C19—O19 = 2.8 (8) and 2.1 (7)°, and C16—O17—C17—C18 = −175.8 (7) and −169 (1)° in (I) and (II), respectively]. The N-formyl side chain is planar in both compounds. The dihedral angles between the two benzene rings are 68.9 (1) and 62.0 (2)° in (I) and (II), respectively. The terminal atom C18 of the ethyl ester side chains of compound (I) shows high anistropic displacement parameters and in compound (II), atoms C17 and C18 show disorder. There is no significant variation in the conformation of the two compounds (Fig. 2), except for the angle between the two phenyl rings and ethyl ester side chains.
A trans-annular hydrogen bond (Damodharan, Syed Ibrahim et al., 2002) (N1—H···O16, connecting the symmetry related molecules) is present in compound (II). Compound (I) is devoid of the trans-annular hydrogen bond due to steric clashes of iodine at para-position with its symmetry-related molecule. Atom N1 in the N-formyl side chain of (I) participates in a three-centered N—H···O interaction with atoms O16 and O19i (Table 1). In compound (II), the N1—H1···O16 and N1—H1···O16i is bifurcated. An C—I···O-type interaction has also been observed in the packing of compound (I) (Fig. 3a). The distance between I13···O16(-x, 1 − y, −z) is 3.333 (4) Å.
The C7—Br7 and C12—Br12 bond lengths are 1.901 (4) and 1.923 (6) Å, respectively, in compound (II), which is longer than the accepted value of 1.89 Å for bromine bonded to a Csp2 atom. The elongation of the C12—Br12 bond may be due to the electron-withdrawing nature of the Br atom (Dewar & Schmeizing, 1969; Leser & Rabinovich, 1978).
A C—Br···O-type interaction is observed in the packing of compound (II) (Fig. 3 b). The Br7···O19(1/2 + x, 1/2 − y, 1/2 + z) distance is 3.053 (3) Å. Hassel & Roming (1962) have also observed the presence of an attractive interaction between a bonded halogen and an O atom. They interpreted it as a charge transfer between an electron-pair donor (O, N or S) and an electron-pair acceptor.