organic compounds
1,3-Bis(propan-2-yl)naphthalene
aCICECO, Departamento de Química, Faculdade de Ciências, Universidade do Aveiro, 3810-193 Aveiro, Portugal, bCIAGEB-Faculdade de Ciências de Saúde, Escola Superior de Saúde da UFP, Universidade Fernando Pessoa, Rua Carlos da Maia, 296, P-4200-150 Porto, Portugal, and cDepartment of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen, AB24 3UE, Scotland.
*Correspondence e-mail: jnlow111@gmail.com
In the title compound, C16H20, one of the isopropyl groups shows almost equal displacements [1.252 (1) and −1.270 (1) Å] of its methyl-C atoms from the mean plane of the naphthalene ring system, while the other shows asymmetric displacements [1.586 (2) and −0.315 (1) Å]. In the crystal, the molecules are linked into sheets lying in the ab plane by three C—H⋯π contacts, two involving donors belonging to the isopropyl groups and the third a donor atom from the naphthalene ring system. The different orientations of the isopropyl groups might be attributed to the fact that the C—H⋯π interaction involving one of them is enhanced by the C—H⋯π interaction involving the aromatic ring.
Related literature
For background to diisopropylnaphthalenes, see: Addison (1983); Brzozowski et al. (2001); Collin et al. (2003).
Experimental
Crystal data
|
Refinement
|
Data collection: APEX2 (Bruker, 2004); cell SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97.
Supporting information
https://doi.org/10.1107/S1600536811047854/hb6496sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536811047854/hb6496Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S1600536811047854/hb6496Isup3.cml
Crystal of C16H20 were obtained from Rütgers Novares GmbH, Duisburg, Germany, with a stated purity greater than 98 percent and used as such.
Molecule (I) crystallized in the orthorhombic system;
Pbca from the H atoms were treated as riding atoms with C—H(aromatic), 0.95 Å, C—H(aliphatic), 1.00 Å, with Uiso = 1.2Ueq(C), C—H(methyl), 0.98 Å,with Uiso = 1.5Ueq(C). The positions of the hydrogen atoms were confirmed in a final difference map.Alkylated naphthalenes have a wide spectrum of applications, ranging from solvents, insulating material, heat transfer fluids, dye works auxiliary and specialty lubricants, (Collin et al., 2003). Due to a variety of novel applications, diisopropylnaphthalene isomers have recently become of interest; they are used in the food packaging industry and as a plant growth regulator; furthermore, they have been introduced as PCB replacement fluids, (Addison,1983). The application of diisopropylnaphthalene isomer mixtures as solvents for carbonless copy paper, in its formulation known as KMC - Kureha Micro Capsule Oil - is of special importance. Some aromatic surfactants are partially based on propylated naphthalenes whose isomeric mixtures are used as water repelling agents for a variety of applications, such as corrosion protections, marine paints, resins,inks, coatings, plasticizers, or electrical, electronic and mechanical applications.
The main components of diisopropylnaphthalene isomer mixtures are 2,6-diisopropylnaphthalene and 2,7-diisopropylnaphthalene, contributing each with ca 40% to the mixture, while a few percent are made of the 1,3-, 1,6- and 1,7-diisopropylnaphthalenes, (Brzozowski et al., 2001). Diisopropylnaphthalenes with isopropyl groups positioned in adjacent ring positions are usually not detected in the mixtures. Separating all isomers or synthesizing them in pure form remains a challenging task.
The 1,3-isomer (I) is shown in Figure 1. The isopropyl methyl groups are oriented cis with respect to atom C2. The naphthalene-isopropyl torsion angles show that the orientations of the isopropyl groups around the C1—C11 and C3—C31 bonds with respect to the naphthalene ring is different in each case, e.g. C2—C1—C11—C111/C112 - 23.24 (17)°/100.54 (14)° and C2—C3—C31—C311/C312 64.27 (16)°/-60.14 (15)°. The orientation of the isopropyl group attached to C1 is unexpected in that unlike the group attached to C3 in which the hydrogen atom attached to C31 lies in the plane of the plane of the naphthalene ring that attached to C11 does not do so.
These orientations position the hydrogen atoms attached to C11 and C31 so that the molecules are linked by three C–H···π contacts to form a sheet lying in the ab plane, Table 1, Figure 2.
For background to diisopropylnaphthalenes, see: Addison (1983); Brzozowski et al. (2001); Collin et al. (2003).
Data collection: APEX2 (Bruker, 2004); cell
SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick 2008).C16H20 | Dx = 1.121 Mg m−3 |
Mr = 212.32 | Mo Kα radiation, λ = 0.71073 Å |
Orthorhombic, Pbca | Cell parameters from 421 reflections |
a = 16.1044 (12) Å | θ = 3.9–23.6° |
b = 8.2099 (5) Å | µ = 0.06 mm−1 |
c = 19.0303 (13) Å | T = 150 K |
V = 2516.1 (3) Å3 | Block, colourless |
Z = 8 | 0.22 × 0.20 × 0.04 mm |
F(000) = 928 |
Bruker SMART APEX CCD diffractometer | 2751 independent reflections |
Radiation source: fine-focus sealed tube | 2240 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.036 |
ω scans | θmax = 27.1°, θmin = 2.5° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | h = −12→20 |
Tmin = 0.986, Tmax = 0.998 | k = −10→8 |
12847 measured reflections | l = −24→18 |
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)] = 0.046 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.108 | H-atom parameters constrained |
S = 1.04 | w = 1/[σ2(Fo2) + (0.0398P)2 + 0.9272P] where P = (Fo2 + 2Fc2)/3 |
2751 reflections | (Δ/σ)max < 0.001 |
145 parameters | Δρmax = 0.19 e Å−3 |
0 restraints | Δρmin = −0.21 e Å−3 |
C16H20 | V = 2516.1 (3) Å3 |
Mr = 212.32 | Z = 8 |
Orthorhombic, Pbca | Mo Kα radiation |
a = 16.1044 (12) Å | µ = 0.06 mm−1 |
b = 8.2099 (5) Å | T = 150 K |
c = 19.0303 (13) Å | 0.22 × 0.20 × 0.04 mm |
Bruker SMART APEX CCD diffractometer | 2751 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | 2240 reflections with I > 2σ(I) |
Tmin = 0.986, Tmax = 0.998 | Rint = 0.036 |
12847 measured reflections |
R[F2 > 2σ(F2)] = 0.046 | 0 restraints |
wR(F2) = 0.108 | H-atom parameters constrained |
S = 1.04 | Δρmax = 0.19 e Å−3 |
2751 reflections | Δρmin = −0.21 e Å−3 |
145 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.35224 (7) | 0.39257 (16) | 0.18964 (7) | 0.0211 (3) | |
C11 | 0.30803 (7) | 0.23796 (16) | 0.16559 (7) | 0.0230 (3) | |
H11 | 0.2519 | 0.2366 | 0.1881 | 0.028* | |
C111 | 0.29530 (9) | 0.22710 (18) | 0.08610 (7) | 0.0321 (3) | |
H11A | 0.2666 | 0.1252 | 0.0746 | 0.048* | |
H11B | 0.3494 | 0.2295 | 0.0625 | 0.048* | |
H11C | 0.2617 | 0.3196 | 0.0702 | 0.048* | |
C112 | 0.35537 (8) | 0.08727 (17) | 0.19147 (8) | 0.0288 (3) | |
H11D | 0.3266 | −0.0114 | 0.1758 | 0.043* | |
H11E | 0.3580 | 0.0885 | 0.2429 | 0.043* | |
H11F | 0.4118 | 0.0884 | 0.1722 | 0.043* | |
C2 | 0.40246 (7) | 0.47957 (16) | 0.14496 (7) | 0.0223 (3) | |
H2 | 0.4066 | 0.4450 | 0.0974 | 0.027* | |
C3 | 0.44854 (7) | 0.61884 (15) | 0.16637 (7) | 0.0221 (3) | |
C31 | 0.50394 (8) | 0.70740 (16) | 0.11426 (7) | 0.0250 (3) | |
H31 | 0.5322 | 0.7979 | 0.1400 | 0.030* | |
C311 | 0.45361 (9) | 0.78327 (18) | 0.05444 (8) | 0.0332 (3) | |
H31A | 0.4912 | 0.8394 | 0.0220 | 0.050* | |
H31B | 0.4138 | 0.8616 | 0.0738 | 0.050* | |
H31C | 0.4236 | 0.6975 | 0.0292 | 0.050* | |
C312 | 0.57143 (8) | 0.59413 (18) | 0.08548 (8) | 0.0314 (3) | |
H31D | 0.6061 | 0.6539 | 0.0519 | 0.047* | |
H31E | 0.5454 | 0.5013 | 0.0618 | 0.047* | |
H31F | 0.6060 | 0.5548 | 0.1243 | 0.047* | |
C4 | 0.44313 (7) | 0.66789 (16) | 0.23492 (7) | 0.0225 (3) | |
H4 | 0.4738 | 0.7604 | 0.2500 | 0.027* | |
C5 | 0.38868 (8) | 0.63261 (16) | 0.35543 (7) | 0.0257 (3) | |
H5 | 0.4211 | 0.7224 | 0.3708 | 0.031* | |
C6 | 0.33889 (8) | 0.55295 (18) | 0.40250 (7) | 0.0283 (3) | |
H6 | 0.3372 | 0.5871 | 0.4502 | 0.034* | |
C7 | 0.29021 (8) | 0.42038 (17) | 0.38021 (7) | 0.0274 (3) | |
H7 | 0.2546 | 0.3671 | 0.4127 | 0.033* | |
C8 | 0.29370 (8) | 0.36748 (17) | 0.31199 (7) | 0.0245 (3) | |
H8 | 0.2609 | 0.2769 | 0.2981 | 0.029* | |
C9 | 0.34551 (7) | 0.44543 (16) | 0.26157 (7) | 0.0211 (3) | |
C10 | 0.39261 (7) | 0.58325 (16) | 0.28397 (7) | 0.0216 (3) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0173 (6) | 0.0207 (6) | 0.0253 (7) | 0.0017 (5) | −0.0029 (5) | −0.0020 (5) |
C11 | 0.0196 (6) | 0.0224 (7) | 0.0270 (7) | −0.0032 (5) | 0.0008 (5) | −0.0018 (6) |
C111 | 0.0374 (8) | 0.0291 (8) | 0.0297 (8) | −0.0099 (6) | −0.0043 (6) | −0.0038 (6) |
C112 | 0.0272 (7) | 0.0230 (7) | 0.0360 (8) | −0.0018 (6) | −0.0002 (6) | −0.0029 (6) |
C2 | 0.0211 (6) | 0.0224 (7) | 0.0232 (6) | 0.0006 (5) | −0.0012 (5) | −0.0023 (6) |
C3 | 0.0198 (6) | 0.0203 (7) | 0.0261 (7) | 0.0007 (5) | −0.0028 (5) | 0.0000 (5) |
C31 | 0.0275 (6) | 0.0212 (7) | 0.0261 (7) | −0.0054 (5) | −0.0002 (5) | −0.0001 (6) |
C311 | 0.0401 (8) | 0.0279 (8) | 0.0317 (8) | 0.0006 (6) | −0.0002 (6) | 0.0036 (6) |
C312 | 0.0277 (7) | 0.0324 (8) | 0.0342 (8) | −0.0036 (6) | 0.0050 (6) | −0.0010 (7) |
C4 | 0.0204 (6) | 0.0191 (6) | 0.0280 (7) | −0.0004 (5) | −0.0041 (5) | −0.0030 (5) |
C5 | 0.0250 (6) | 0.0243 (7) | 0.0280 (7) | 0.0024 (5) | −0.0045 (5) | −0.0052 (6) |
C6 | 0.0276 (7) | 0.0324 (8) | 0.0248 (7) | 0.0061 (6) | −0.0003 (5) | −0.0050 (6) |
C7 | 0.0230 (6) | 0.0314 (8) | 0.0279 (7) | 0.0023 (6) | 0.0032 (5) | 0.0015 (6) |
C8 | 0.0193 (6) | 0.0257 (7) | 0.0285 (7) | −0.0005 (5) | −0.0005 (5) | −0.0017 (6) |
C9 | 0.0164 (6) | 0.0212 (6) | 0.0257 (7) | 0.0035 (5) | −0.0020 (5) | −0.0012 (5) |
C10 | 0.0182 (6) | 0.0211 (7) | 0.0253 (7) | 0.0042 (5) | −0.0035 (5) | −0.0024 (5) |
C1—C2 | 1.3738 (18) | C311—H31A | 0.9800 |
C1—C9 | 1.4400 (18) | C311—H31B | 0.9800 |
C1—C11 | 1.5256 (18) | C311—H31C | 0.9800 |
C11—C111 | 1.5291 (19) | C312—H31D | 0.9800 |
C11—C112 | 1.5344 (19) | C312—H31E | 0.9800 |
C11—H11 | 1.0000 | C312—H31F | 0.9800 |
C111—H11A | 0.9800 | C4—C10 | 1.4199 (18) |
C111—H11B | 0.9800 | C4—H4 | 0.9500 |
C111—H11C | 0.9800 | C5—C6 | 1.369 (2) |
C112—H11D | 0.9800 | C5—C10 | 1.4203 (18) |
C112—H11E | 0.9800 | C5—H5 | 0.9500 |
C112—H11F | 0.9800 | C6—C7 | 1.407 (2) |
C2—C3 | 1.4228 (17) | C6—H6 | 0.9500 |
C2—H2 | 0.9500 | C7—C8 | 1.3701 (19) |
C3—C4 | 1.3680 (18) | C7—H7 | 0.9500 |
C3—C31 | 1.5193 (18) | C8—C9 | 1.4236 (18) |
C31—C311 | 1.5299 (19) | C8—H8 | 0.9500 |
C31—C312 | 1.5318 (19) | C9—C10 | 1.4273 (18) |
C31—H31 | 1.0000 | ||
C2—C1—C9 | 118.42 (12) | C31—C311—H31A | 109.5 |
C2—C1—C11 | 121.44 (12) | C31—C311—H31B | 109.5 |
C9—C1—C11 | 120.05 (11) | H31A—C311—H31B | 109.5 |
C1—C11—C111 | 114.07 (11) | C31—C311—H31C | 109.5 |
C1—C11—C112 | 110.04 (10) | H31A—C311—H31C | 109.5 |
C111—C11—C112 | 109.70 (11) | H31B—C311—H31C | 109.5 |
C1—C11—H11 | 107.6 | C31—C312—H31D | 109.5 |
C111—C11—H11 | 107.6 | C31—C312—H31E | 109.5 |
C112—C11—H11 | 107.6 | H31D—C312—H31E | 109.5 |
C11—C111—H11A | 109.5 | C31—C312—H31F | 109.5 |
C11—C111—H11B | 109.5 | H31D—C312—H31F | 109.5 |
H11A—C111—H11B | 109.5 | H31E—C312—H31F | 109.5 |
C11—C111—H11C | 109.5 | C3—C4—C10 | 121.29 (12) |
H11A—C111—H11C | 109.5 | C3—C4—H4 | 119.4 |
H11B—C111—H11C | 109.5 | C10—C4—H4 | 119.4 |
C11—C112—H11D | 109.5 | C6—C5—C10 | 121.09 (13) |
C11—C112—H11E | 109.5 | C6—C5—H5 | 119.5 |
H11D—C112—H11E | 109.5 | C10—C5—H5 | 119.5 |
C11—C112—H11F | 109.5 | C5—C6—C7 | 119.93 (13) |
H11D—C112—H11F | 109.5 | C5—C6—H6 | 120.0 |
H11E—C112—H11F | 109.5 | C7—C6—H6 | 120.0 |
C1—C2—C3 | 123.20 (12) | C8—C7—C6 | 120.54 (13) |
C1—C2—H2 | 118.4 | C8—C7—H7 | 119.7 |
C3—C2—H2 | 118.4 | C6—C7—H7 | 119.7 |
C4—C3—C2 | 118.45 (12) | C7—C8—C9 | 121.34 (13) |
C4—C3—C31 | 121.27 (12) | C7—C8—H8 | 119.3 |
C2—C3—C31 | 120.26 (12) | C9—C8—H8 | 119.3 |
C3—C31—C311 | 111.68 (11) | C8—C9—C10 | 117.81 (12) |
C3—C31—C312 | 111.07 (11) | C8—C9—C1 | 123.32 (12) |
C311—C31—C312 | 110.93 (12) | C10—C9—C1 | 118.87 (11) |
C3—C31—H31 | 107.7 | C4—C10—C5 | 121.02 (12) |
C311—C31—H31 | 107.7 | C4—C10—C9 | 119.74 (12) |
C312—C31—H31 | 107.7 | C5—C10—C9 | 119.24 (12) |
C2—C1—C11—C111 | −23.24 (17) | C6—C7—C8—C9 | −0.8 (2) |
C9—C1—C11—C111 | 160.20 (12) | C7—C8—C9—C10 | −1.32 (18) |
C2—C1—C11—C112 | 100.54 (14) | C7—C8—C9—C1 | 178.96 (12) |
C9—C1—C11—C112 | −76.03 (14) | C2—C1—C9—C8 | 178.25 (12) |
C9—C1—C2—C3 | 0.37 (18) | C11—C1—C9—C8 | −5.08 (18) |
C11—C1—C2—C3 | −176.25 (11) | C2—C1—C9—C10 | −1.47 (17) |
C1—C2—C3—C4 | 0.52 (19) | C11—C1—C9—C10 | 175.20 (11) |
C1—C2—C3—C31 | 179.01 (12) | C3—C4—C10—C5 | 178.59 (12) |
C4—C3—C31—C311 | −117.29 (14) | C3—C4—C10—C9 | −0.82 (18) |
C2—C3—C31—C311 | 64.27 (16) | C6—C5—C10—C4 | 178.83 (12) |
C4—C3—C31—C312 | 118.31 (14) | C6—C5—C10—C9 | −1.76 (19) |
C2—C3—C31—C312 | −60.14 (15) | C8—C9—C10—C4 | −178.04 (11) |
C2—C3—C4—C10 | −0.29 (18) | C1—C9—C10—C4 | 1.70 (17) |
C31—C3—C4—C10 | −178.76 (11) | C8—C9—C10—C5 | 2.54 (17) |
C10—C5—C6—C7 | −0.3 (2) | C1—C9—C10—C5 | −177.73 (11) |
C5—C6—C7—C8 | 1.6 (2) |
Cg1 and Cg2 are the centroids of the C1–C4/C9/C10 and C5–C10 rings, respectively. |
D—H···A | D—H | H···A | D···A | D—H···A |
C8—H8···Cg2i | 0.95 | 2.88 | 3.7399 (15) | 151 |
C11—H11···Cg1i | 1.00 | 2.98 | 3.8289 (13) | 144 |
C31—H31···Cg2ii | 1.00 | 2.68 | 3.6048 (14) | 155 |
Symmetry codes: (i) x, −y−3/2, z−1/2; (ii) x+3/2, −y+1/2, −z. |
Experimental details
Crystal data | |
Chemical formula | C16H20 |
Mr | 212.32 |
Crystal system, space group | Orthorhombic, Pbca |
Temperature (K) | 150 |
a, b, c (Å) | 16.1044 (12), 8.2099 (5), 19.0303 (13) |
V (Å3) | 2516.1 (3) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 0.06 |
Crystal size (mm) | 0.22 × 0.20 × 0.04 |
Data collection | |
Diffractometer | Bruker SMART APEX CCD |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2003) |
Tmin, Tmax | 0.986, 0.998 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 12847, 2751, 2240 |
Rint | 0.036 |
(sin θ/λ)max (Å−1) | 0.641 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.046, 0.108, 1.04 |
No. of reflections | 2751 |
No. of parameters | 145 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.19, −0.21 |
Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009), SHELXL97 (Sheldrick 2008).
Cg1 and Cg2 are the centroids of the C1–C4/C9/C10 and C5–C10 rings, respectively. |
D—H···A | D—H | H···A | D···A | D—H···A |
C8—H8···Cg2i | 0.95 | 2.88 | 3.7399 (15) | 151 |
C11—H11···Cg1i | 1.00 | 2.98 | 3.8289 (13) | 144 |
C31—H31···Cg2ii | 1.00 | 2.68 | 3.6048 (14) | 155 |
Symmetry codes: (i) x, −y−3/2, z−1/2; (ii) x+3/2, −y+1/2, −z. |
Acknowledgements
The authors are grateful to Dr Bernd Godry and Rütgers Novares GmbH for the donation of a sample of the title compound. BS acknowledges the Fundação para a Ciência e a Tecnologia (FCT) and the European Social Fund (ESF) under the 3rd Community Support Framework (CSF) for the award of a post-doctoral grant (grant No. SFRH/BPD/38637/2007) and the award of research project PTDC/AAC-AMB/121161/2010.
References
Addison, R. F. (1983). Environ. Sci. Technol. 17, 486A–494A. CrossRef CAS PubMed Web of Science Google Scholar
Bruker (2004). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Brzozowski, R., Dobrowolski, J. C., Jamróz, M. H. & Skupiński, W. (2001). J. Mol. Catal. A, 170, 95–99. CrossRef CAS Google Scholar
Collin, G., Höke, H. & Greim, H. (2003). Naphthalene and Hydronaphthalenes. In Ullmann's Encyclopedia of Industrial Chemistry. Weilheim: Wiley-VCH. Google Scholar
Sheldrick, G. M. (2003). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
Alkylated naphthalenes have a wide spectrum of applications, ranging from solvents, insulating material, heat transfer fluids, dye works auxiliary and specialty lubricants, (Collin et al., 2003). Due to a variety of novel applications, diisopropylnaphthalene isomers have recently become of interest; they are used in the food packaging industry and as a plant growth regulator; furthermore, they have been introduced as PCB replacement fluids, (Addison,1983). The application of diisopropylnaphthalene isomer mixtures as solvents for carbonless copy paper, in its formulation known as KMC - Kureha Micro Capsule Oil - is of special importance. Some aromatic surfactants are partially based on propylated naphthalenes whose isomeric mixtures are used as water repelling agents for a variety of applications, such as corrosion protections, marine paints, resins,inks, coatings, plasticizers, or electrical, electronic and mechanical applications.
The main components of diisopropylnaphthalene isomer mixtures are 2,6-diisopropylnaphthalene and 2,7-diisopropylnaphthalene, contributing each with ca 40% to the mixture, while a few percent are made of the 1,3-, 1,6- and 1,7-diisopropylnaphthalenes, (Brzozowski et al., 2001). Diisopropylnaphthalenes with isopropyl groups positioned in adjacent ring positions are usually not detected in the mixtures. Separating all isomers or synthesizing them in pure form remains a challenging task.
The 1,3-isomer (I) is shown in Figure 1. The isopropyl methyl groups are oriented cis with respect to atom C2. The naphthalene-isopropyl torsion angles show that the orientations of the isopropyl groups around the C1—C11 and C3—C31 bonds with respect to the naphthalene ring is different in each case, e.g. C2—C1—C11—C111/C112 - 23.24 (17)°/100.54 (14)° and C2—C3—C31—C311/C312 64.27 (16)°/-60.14 (15)°. The orientation of the isopropyl group attached to C1 is unexpected in that unlike the group attached to C3 in which the hydrogen atom attached to C31 lies in the plane of the plane of the naphthalene ring that attached to C11 does not do so.
These orientations position the hydrogen atoms attached to C11 and C31 so that the molecules are linked by three C–H···π contacts to form a sheet lying in the ab plane, Table 1, Figure 2.