In the title compound, N6-benzyladenine hydrobromide [N6-benzyladeninium bromide], C12H12N5+·Br-, the adenine moiety exists as the N3-protonated N7-H tautomer. The N6 substituent is distal to N7 and the phenyl ring makes a dihedral angle of 108.43 (12)° with the adenine plane. Thus, protonation of benzyladenine does not affect the conformational requirements for cytokinin activity. The conformation of the title compound has been compared with other cytokinins.
Supporting information
CCDC reference: 172220
Key indicators
- Single-crystal X-ray study
- T = 293 K
- Mean (C-C) = 0.014 Å
- R factor = 0.067
- wR factor = 0.173
- Data-to-parameter ratio = 7.5
checkCIF results
No syntax errors found
ADDSYM reports no extra symmetry
Alert Level A:
REFLT_03
From the CIF: _diffrn_reflns_theta_max 69.90
From the CIF: _reflns_number_total 1556
TEST2: Reflns within _diffrn_reflns_theta_max
Count of symmetry unique reflns 2428
Completeness (_total/calc) 64.09%
Alert A: < 85% complete (theta max?)
Alert Level C:
RINTA_01 Alert C The value of Rint is greater than 0.10
Rint given 0.106
General Notes
ABSTM_02 When printed, the submitted absorption T values will be replaced
by the scaled T values. Since the ratio of scaled T's is
identical to the ratio of reported T values, the scaling does
not imply a change to the absorption corrections used in the
study.
Ratio of Tmax expected/reported 1.075
Tmax scaled 0.524 Tmin scaled 0.352
1 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
1 Alert Level C = Please check
N6-Benzyladenine (Loba Chemie, India) was dissolved in the minimum
amount of dilute hydrobromic acid and recrystalliz ed from a
methanol/n-pentane mixture.
Data collection: DIFABS (Walker & Stuart, 1983); cell refinement: DIFABS (Walker & Stuart, 1983); data reduction: DIFABS (Walker & Stuart, 1983); program(s) used to solve structure: SHELXS97 (sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ZORTEP97 (Zsolnai, 1997); software used to prepare material for publication: PLATON (Spek, 1990).
Crystal data top
C12H12BrN5 | F(000) = 616 |
Mr = 306.16 | Dx = 1.592 Mg m−3 |
Monoclinic, P21/c | Cu Kα radiation, λ = 1.54178 Å |
a = 18.581 (3) Å | Cell parameters from 40 reflections |
b = 5.163 (2) Å | θ = 6.8–16.3° |
c = 13.344 (3) Å | µ = 4.31 mm−1 |
β = 93.71 (2)° | T = 293 K |
V = 1277.5 (6) Å3 | Needle, colourless |
Z = 4 | 0.33 × 0.18 × 0.15 mm |
Data collection top
Siemens AED diffractometer | Rint = 0.106 |
ω–2θ scans | θmax = 69.9°, θmin = 4.8° |
Absorption correction: part of the refinement model (ΔF) (Parkin et al., 1995) | h = −22→22 |
Tmin = 0.327, Tmax = 0.488 | k = 0→6 |
1608 measured reflections | l = −16→15 |
1556 independent reflections | 3 standard reflections every 60 min |
1556 reflections with I > 2σ(I) | intensity decay: none |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.067 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.173 | w = 1/[σ2(Fo2) + (0.0956P)2 + 1.1524P] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max < 0.001 |
1556 reflections | Δρmax = 0.94 e Å−3 |
208 parameters | Δρmin = −1.44 e Å−3 |
0 restraints | Extinction correction: SHELXL97 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0025 (5) |
Crystal data top
C12H12BrN5 | V = 1277.5 (6) Å3 |
Mr = 306.16 | Z = 4 |
Monoclinic, P21/c | Cu Kα radiation |
a = 18.581 (3) Å | µ = 4.31 mm−1 |
b = 5.163 (2) Å | T = 293 K |
c = 13.344 (3) Å | 0.33 × 0.18 × 0.15 mm |
β = 93.71 (2)° | |
Data collection top
Siemens AED diffractometer | 1556 reflections with I > 2σ(I) |
Absorption correction: part of the refinement model (ΔF) (Parkin et al., 1995) | Rint = 0.106 |
Tmin = 0.327, Tmax = 0.488 | 3 standard reflections every 60 min |
1608 measured reflections | intensity decay: none |
1556 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.067 | 0 restraints |
wR(F2) = 0.173 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.04 | Δρmax = 0.94 e Å−3 |
1556 reflections | Δρmin = −1.44 e Å−3 |
208 parameters | |
Special details top
Geometry. Bond distances, angles etc. have been calculated using the rounded
fractional coordinates. All e.s.d.'s are estimated from the variances of the
(full) variance-covariance matrix. The cell e.s.d.'s are taken into account in
the estimation of distances, angles and torsion angles |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Br1 | 0.16929 (4) | 0.53176 (16) | 0.30710 (5) | 0.0596 (3) | |
N1 | 0.2273 (3) | 0.2989 (12) | 0.0426 (4) | 0.057 (2) | |
N3 | 0.1098 (4) | 0.4556 (12) | 0.0018 (4) | 0.0560 (19) | |
N6 | 0.2478 (4) | −0.0404 (15) | 0.1532 (5) | 0.0603 (19) | |
N7 | 0.0819 (3) | −0.0472 (14) | 0.1658 (4) | 0.055 (2) | |
N9 | 0.0124 (4) | 0.2408 (13) | 0.0828 (4) | 0.061 (2) | |
C2 | 0.1815 (5) | 0.4583 (16) | −0.0052 (5) | 0.061 (2) | |
C4 | 0.0817 (4) | 0.2757 (14) | 0.0612 (5) | 0.053 (2) | |
C5 | 0.1274 (4) | 0.0999 (13) | 0.1106 (5) | 0.049 (2) | |
C6 | 0.2020 (4) | 0.1146 (14) | 0.1031 (5) | 0.051 (2) | |
C8 | 0.0158 (4) | 0.0417 (17) | 0.1466 (5) | 0.059 (3) | |
C10 | 0.3251 (5) | −0.033 (3) | 0.1476 (8) | 0.087 (4) | |
C11 | 0.3635 (4) | −0.0937 (18) | 0.2487 (6) | 0.062 (3) | |
C12 | 0.3496 (6) | 0.039 (2) | 0.3326 (8) | 0.081 (3) | |
C13 | 0.3846 (6) | −0.021 (2) | 0.4229 (8) | 0.090 (4) | |
C14 | 0.4354 (6) | −0.207 (3) | 0.4295 (8) | 0.100 (5) | |
C15 | 0.4499 (6) | −0.347 (3) | 0.3451 (9) | 0.096 (5) | |
C16 | 0.4131 (5) | −0.289 (2) | 0.2542 (7) | 0.071 (3) | |
H2 | 0.200 (4) | 0.601 (17) | −0.047 (6) | 0.06 (2)* | |
H3 | 0.084 (4) | 0.567 (13) | −0.032 (5) | 0.040 (18)* | |
H6 | 0.234 (3) | −0.178 (14) | 0.182 (5) | 0.042 (18)* | |
H7 | 0.094 (3) | −0.167 (13) | 0.197 (5) | 0.031 (17)* | |
H8 | −0.024 (5) | −0.024 (15) | 0.171 (7) | 0.07 (3)* | |
H10A | 0.333 (8) | −0.18 (3) | 0.090 (11) | 0.17 (6)* | |
H10B | 0.335 (5) | 0.125 (18) | 0.135 (7) | 0.06 (3)* | |
H12 | 0.314 (4) | 0.178 (17) | 0.328 (6) | 0.07 (2)* | |
H13 | 0.37318 | 0.06793 | 0.48036 | 0.1078* | |
H14 | 0.455 (8) | −0.27 (3) | 0.474 (11) | 0.17 (7)* | |
H15 | 0.486 (6) | −0.47 (2) | 0.345 (8) | 0.10 (4)* | |
H16 | 0.420 (6) | −0.40 (3) | 0.203 (9) | 0.11 (4)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Br1 | 0.0661 (6) | 0.0654 (6) | 0.0464 (5) | 0.0064 (4) | −0.0025 (3) | 0.0038 (3) |
N1 | 0.067 (4) | 0.063 (4) | 0.041 (3) | −0.004 (3) | −0.003 (3) | 0.004 (3) |
N3 | 0.070 (4) | 0.051 (3) | 0.045 (3) | 0.004 (3) | −0.012 (3) | 0.007 (3) |
N6 | 0.054 (3) | 0.075 (4) | 0.051 (3) | 0.003 (3) | −0.004 (3) | 0.020 (3) |
N7 | 0.059 (4) | 0.056 (4) | 0.049 (3) | 0.007 (3) | −0.009 (3) | 0.007 (3) |
N9 | 0.062 (4) | 0.069 (4) | 0.052 (3) | 0.012 (3) | −0.006 (3) | 0.002 (3) |
C2 | 0.078 (5) | 0.062 (4) | 0.042 (3) | −0.003 (4) | −0.006 (3) | 0.003 (3) |
C4 | 0.062 (4) | 0.052 (4) | 0.044 (3) | 0.001 (3) | −0.011 (3) | −0.006 (3) |
C5 | 0.061 (4) | 0.047 (4) | 0.038 (3) | −0.003 (3) | −0.002 (3) | 0.000 (3) |
C6 | 0.061 (4) | 0.052 (4) | 0.038 (3) | 0.002 (3) | −0.006 (3) | 0.000 (3) |
C8 | 0.050 (4) | 0.076 (5) | 0.050 (4) | 0.006 (4) | −0.002 (3) | 0.002 (3) |
C10 | 0.058 (5) | 0.132 (11) | 0.071 (6) | 0.015 (6) | 0.006 (4) | 0.039 (7) |
C11 | 0.047 (4) | 0.078 (5) | 0.062 (4) | −0.002 (4) | 0.001 (3) | 0.020 (4) |
C12 | 0.072 (5) | 0.088 (7) | 0.082 (6) | 0.024 (5) | 0.003 (4) | 0.002 (5) |
C13 | 0.091 (7) | 0.109 (8) | 0.068 (5) | 0.018 (6) | −0.005 (5) | −0.017 (5) |
C14 | 0.072 (6) | 0.161 (13) | 0.064 (6) | 0.008 (7) | −0.008 (5) | 0.028 (7) |
C15 | 0.071 (6) | 0.129 (10) | 0.086 (7) | 0.038 (7) | −0.002 (5) | 0.032 (7) |
C16 | 0.069 (5) | 0.085 (6) | 0.059 (5) | 0.014 (5) | 0.009 (4) | 0.006 (4) |
Geometric parameters (Å, º) top
N1—C2 | 1.318 (10) | C11—C16 | 1.365 (13) |
N1—C6 | 1.352 (9) | C11—C12 | 1.352 (13) |
N3—C2 | 1.342 (12) | C12—C13 | 1.367 (15) |
N3—C4 | 1.348 (9) | C13—C14 | 1.345 (17) |
N6—C6 | 1.318 (10) | C14—C15 | 1.379 (18) |
N6—C10 | 1.444 (12) | C15—C16 | 1.386 (15) |
N7—C5 | 1.384 (9) | C2—H2 | 1.00 (8) |
N7—C8 | 1.321 (10) | C8—H8 | 0.89 (9) |
N9—C4 | 1.350 (10) | C10—H10A | 1.10 (15) |
N9—C8 | 1.334 (10) | C10—H10B | 0.86 (9) |
N3—H3 | 0.86 (7) | C12—H12 | 0.98 (8) |
N6—H6 | 0.85 (7) | C13—H13 | 0.9299 |
N7—H7 | 0.77 (7) | C14—H14 | 0.75 (15) |
C4—C5 | 1.381 (10) | C15—H15 | 0.92 (11) |
C5—C6 | 1.398 (11) | C16—H16 | 0.91 (13) |
C10—C11 | 1.517 (13) | | |
| | | |
Br1···N6i | 3.408 (7) | C5···Br1 | 3.491 (7) |
Br1···N7i | 3.244 (6) | C6···Br1 | 3.554 (7) |
Br1···C5 | 3.491 (7) | C8···Br1x | 3.534 (8) |
Br1···C6 | 3.554 (7) | C8···N9vii | 3.401 (9) |
Br1···C8ii | 3.534 (8) | C8···H3v | 3.08 (7) |
Br1···C2iii | 3.557 (8) | C12···H6 | 3.06 (6) |
Br1···C2iv | 3.631 (8) | C13···H10Axi | 2.92 (15) |
Br1···H7i | 2.50 (6) | C14···H10Axi | 3.01 (15) |
Br1···H8ii | 2.75 (9) | C16···H15xii | 2.88 (11) |
Br1···H12 | 3.25 (8) | H2···Br1ix | 2.75 (8) |
Br1···H6i | 2.60 (7) | H3···N9v | 2.12 (7) |
Br1···H2iv | 2.75 (8) | H3···C8v | 3.08 (7) |
N3···N9v | 2.925 (10) | H6···Br1vi | 2.60 (7) |
N6···N7 | 3.098 (9) | H6···N7 | 2.90 (6) |
N6···Br1vi | 3.408 (7) | H6···C12 | 3.06 (6) |
N7···N6 | 3.098 (9) | H7···Br1vi | 2.50 (6) |
N7···Br1vi | 3.244 (6) | H8···Br1x | 2.75 (9) |
N9···C8vii | 3.401 (9) | H10A···H16 | 2.42 (19) |
N9···N3v | 2.925 (10) | H10A···C13xiii | 2.92 (15) |
N1···H10B | 2.45 (9) | H10A···C14xiii | 3.01 (15) |
N6···H12 | 2.80 (8) | H10B···N1 | 2.45 (9) |
N7···H6 | 2.90 (6) | H12···Br1 | 3.25 (8) |
N9···H3v | 2.12 (7) | H12···N6 | 2.80 (8) |
C2···Br1viii | 3.557 (8) | H15···C16xiv | 2.88 (11) |
C2···Br1ix | 3.631 (8) | H16···H10A | 2.42 (19) |
| | | |
C2—N1—C6 | 119.3 (6) | C12—C11—C16 | 119.6 (8) |
C2—N3—C4 | 118.2 (7) | C11—C12—C13 | 120.6 (10) |
C6—N6—C10 | 124.7 (8) | C12—C13—C14 | 120.7 (10) |
C5—N7—C8 | 107.4 (6) | C13—C14—C15 | 119.6 (11) |
C4—N9—C8 | 103.5 (6) | C14—C15—C16 | 119.3 (12) |
C4—N3—H3 | 123 (5) | C11—C16—C15 | 120.0 (10) |
C2—N3—H3 | 119 (5) | N1—C2—H2 | 120 (4) |
C10—N6—H6 | 112 (4) | N3—C2—H2 | 115 (4) |
C6—N6—H6 | 122 (4) | N7—C8—H8 | 125 (6) |
C5—N7—H7 | 124 (4) | N9—C8—H8 | 121 (6) |
C8—N7—H7 | 128 (4) | N6—C10—H10A | 101 (8) |
N1—C2—N3 | 124.9 (7) | N6—C10—H10B | 105 (6) |
N9—C4—C5 | 112.1 (6) | C11—C10—H10A | 114 (8) |
N3—C4—N9 | 129.0 (7) | C11—C10—H10B | 106 (6) |
N3—C4—C5 | 118.9 (7) | H10A—C10—H10B | 119 (11) |
N7—C5—C4 | 103.7 (6) | C11—C12—H12 | 119 (5) |
C4—C5—C6 | 120.8 (6) | C13—C12—H12 | 120 (5) |
N7—C5—C6 | 135.3 (6) | C12—C13—H13 | 119.60 |
N1—C6—N6 | 119.5 (7) | C14—C13—H13 | 119.67 |
N6—C6—C5 | 122.8 (7) | C13—C14—H14 | 132 (11) |
N1—C6—C5 | 117.8 (6) | C15—C14—H14 | 108 (11) |
N7—C8—N9 | 113.4 (7) | C14—C15—H15 | 123 (7) |
N6—C10—C11 | 111.1 (8) | C16—C15—H15 | 118 (7) |
C10—C11—C12 | 121.8 (9) | C11—C16—H16 | 124 (8) |
C10—C11—C16 | 118.5 (9) | C15—C16—H16 | 116 (9) |
| | | |
C6—N1—C2—N3 | 0.7 (11) | N9—C4—C5—C6 | −175.9 (6) |
C2—N1—C6—N6 | −178.1 (7) | N9—C4—C5—N7 | −0.5 (8) |
C2—N1—C6—C5 | 1.0 (10) | C4—C5—C6—N6 | 176.3 (7) |
C4—N3—C2—N1 | −0.7 (11) | C4—C5—C6—N1 | −2.8 (10) |
C2—N3—C4—N9 | 177.4 (7) | N7—C5—C6—N1 | −176.4 (7) |
C2—N3—C4—C5 | −1.2 (10) | N7—C5—C6—N6 | 2.7 (13) |
C10—N6—C6—N1 | −1.1 (12) | N6—C10—C11—C16 | 125.5 (10) |
C10—N6—C6—C5 | 179.8 (9) | N6—C10—C11—C12 | −54.2 (15) |
C6—N6—C10—C11 | 144.2 (9) | C10—C11—C12—C13 | 179.5 (10) |
C8—N7—C5—C4 | 0.6 (8) | C16—C11—C12—C13 | −0.2 (15) |
C8—N7—C5—C6 | 174.9 (8) | C10—C11—C16—C15 | 179.1 (10) |
C5—N7—C8—N9 | −0.5 (9) | C12—C11—C16—C15 | −1.2 (15) |
C8—N9—C4—N3 | −178.4 (7) | C11—C12—C13—C14 | 2.4 (17) |
C8—N9—C4—C5 | 0.3 (8) | C12—C13—C14—C15 | −3.1 (19) |
C4—N9—C8—N7 | 0.2 (8) | C13—C14—C15—C16 | 1.6 (19) |
N3—C4—C5—N7 | 178.3 (6) | C14—C15—C16—C11 | 0.5 (17) |
N3—C4—C5—C6 | 2.9 (10) | | |
Symmetry codes: (i) x, y+1, z; (ii) −x, y+1/2, −z+1/2; (iii) x, −y+1/2, z+1/2; (iv) x, −y+3/2, z+1/2; (v) −x, −y+1, −z; (vi) x, y−1, z; (vii) −x, −y, −z; (viii) x, −y+1/2, z−1/2; (ix) x, −y+3/2, z−1/2; (x) −x, y−1/2, −z+1/2; (xi) x, −y−1/2, z+1/2; (xii) −x+1, y+1/2, −z+1/2; (xiii) x, −y−1/2, z−1/2; (xiv) −x+1, y−1/2, −z+1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H3···N9v | 0.86 (7) | 2.12 (7) | 2.925 (10) | 156 (7) |
N6—H6···Br1vi | 0.85 (7) | 2.60 (7) | 3.408 (7) | 159 (6) |
N7—H7···Br1vi | 0.77 (7) | 2.50 (6) | 3.244 (6) | 161 (5) |
C2—H2···Br1ix | 1.00 (8) | 2.75 (8) | 3.631 (8) | 147 (6) |
C8—H8···Br1x | 0.89 (9) | 2.75 (9) | 3.534 (8) | 147 (7) |
C10—H10B···N1 | 0.86 (9) | 2.45 (9) | 2.806 (14) | 106 (7) |
Symmetry codes: (v) −x, −y+1, −z; (vi) x, y−1, z; (ix) x, −y+3/2, z−1/2; (x) −x, y−1/2, −z+1/2. |
Experimental details
Crystal data |
Chemical formula | C12H12BrN5 |
Mr | 306.16 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 293 |
a, b, c (Å) | 18.581 (3), 5.163 (2), 13.344 (3) |
β (°) | 93.71 (2) |
V (Å3) | 1277.5 (6) |
Z | 4 |
Radiation type | Cu Kα |
µ (mm−1) | 4.31 |
Crystal size (mm) | 0.33 × 0.18 × 0.15 |
|
Data collection |
Diffractometer | Siemens AED diffractometer |
Absorption correction | Part of the refinement model (ΔF) (Parkin et al., 1995) |
Tmin, Tmax | 0.327, 0.488 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1608, 1556, 1556 |
Rint | 0.106 |
(sin θ/λ)max (Å−1) | 0.609 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.067, 0.173, 1.04 |
No. of reflections | 1556 |
No. of parameters | 208 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.94, −1.44 |
Selected geometric parameters (Å, º) topN1—C2 | 1.318 (10) | N6—C10 | 1.444 (12) |
N1—C6 | 1.352 (9) | N7—C5 | 1.384 (9) |
N3—C2 | 1.342 (12) | N7—C8 | 1.321 (10) |
N3—C4 | 1.348 (9) | N9—C4 | 1.350 (10) |
N6—C6 | 1.318 (10) | N9—C8 | 1.334 (10) |
| | | |
C2—N1—C6 | 119.3 (6) | N3—C4—C5 | 118.9 (7) |
C2—N3—C4 | 118.2 (7) | N7—C5—C4 | 103.7 (6) |
C6—N6—C10 | 124.7 (8) | N7—C5—C6 | 135.3 (6) |
C5—N7—C8 | 107.4 (6) | N1—C6—N6 | 119.5 (7) |
C4—N9—C8 | 103.5 (6) | N6—C6—C5 | 122.8 (7) |
N1—C2—N3 | 124.9 (7) | N1—C6—C5 | 117.8 (6) |
N9—C4—C5 | 112.1 (6) | N7—C8—N9 | 113.4 (7) |
N3—C4—N9 | 129.0 (7) | N6—C10—C11 | 111.1 (8) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H3···N9i | 0.86 (7) | 2.12 (7) | 2.925 (10) | 156 (7) |
N6—H6···Br1ii | 0.85 (7) | 2.60 (7) | 3.408 (7) | 159 (6) |
N7—H7···Br1ii | 0.77 (7) | 2.50 (6) | 3.244 (6) | 161 (5) |
C2—H2···Br1iii | 1.00 (8) | 2.75 (8) | 3.631 (8) | 147 (6) |
C8—H8···Br1iv | 0.89 (9) | 2.75 (9) | 3.534 (8) | 147 (7) |
C10—H10B···N1 | 0.86 (9) | 2.45 (9) | 2.806 (14) | 106 (7) |
Symmetry codes: (i) −x, −y+1, −z; (ii) x, y−1, z; (iii) x, −y+3/2, z−1/2; (iv) −x, y−1/2, −z+1/2. |
Many N6-substituted adenine derivatives function as plant growth stimulants (Hall, 1973). Kinetin (N6-furfurylaminopurine) is one of the naturally occurring cytokinins. Some of the N6-substituted adenines synthesized also show cytokinin activity depending upon their conformation (Pattabhi, 1990). N6-Benzyladenine hydrobromide (BABR), (I), has been investigated to explore the conformation of this molecule in a variety of crystalline and chemical environments. The ZORTEP diagram (Zsolnai, 1997) of the molecule with the atom-labeling scheme is shown in Fig. 1.
N6-Benzyladenine exists as the N9—H tautomer in the crystal structure (Ragunathan et al., 1983). In monoprotonated adenine systems, N1 is the protonation site (Voet & Rich, 1970). However, in this crystal structure, very interestingly, adenine moiety exists as the N7—H tautomer with the proton at N3. The H atoms at N7 and N3 were located in the difference Fourier map. Further evidence for the presence of the H atoms on these sites comes from the enhancement of the corresponding internal bond angles. The enhancement of the internal bond angles on protonation sites has been already well established (Taylor & Kennard, 1982). In the crystal structure of a copper complex of benzyladenine (Balasubramanian et al., 1996) also, which was prepared under slightly acidic conditions, the adenine moieties exist as the N7—H tautomer with protonation at N3 and coordination at N9. In BABR, the internal angle at N9 is 103.2 (7)°, which agrees well with that observed in N6-benzyladenine existing as N7—H tautomer. In the crystal structure of N6-benzoyladenine (Ragunathan & Pattabhi, 1981), the adeinine moiety exists as the N7—H tautomer rather than the normal N9—H tautomer for neutral adenines and this is due to intramolecular hydrogen bonding. It has been suggested that a free N1 position is one of the requirements for cytokinin activity and it is interesting to note that the N1 position is maintained free even under acidic conditions/metal binding namely in BABR and a copper complex of N6-benzyladenine. [Please clarify this wording]
There is no significant base stacking. This is in agreement with the packing patterns of other cytokinins previously reported. The molecules are packed by N—H···N and N—H···Br interactions.
The dihedral angle between the adenine plane and the phenyl-ring plane is 108.43 (12)°. This is in agreement with the range of values nearly 90° proposed for cytokinin activity. The N6 substituent is also distal to N7 as in other cytokinins (Sariano-Garcia & Parthasarathi, 1977; Ragunathan & Pattabhi, 1981; Bugg & Thewalt, 1972; McMullan & Sundaralingam, 1971; Walker & Tollin, 1982). Thus, a free N1, distal conformation of the N6 substituent with respect to N7, absence of base stacking and a near 90° value of the dihedral angle (between the adenine ring and the plane of the N6-substituent) seem to be necessary conditions for cytokinin activity.