2-(4-tert-Butylphenyl)-5-p-tolyl-1,3,4-oxadiazole

In the title compound, C19H20N2O, the dihedral angles between the 1,3,4-oxadiazole ring and the pendant 4-tert-butylphenyl and 4-methylphenyl rings are 12.53 (17) and 2.14 (17)°, respectively. In the crystal, molecules are linked by C—H⋯N hydrogen bonds, forming chains.


S1. Experimental
To a 100 ml three-neck flask, 4-tert-Butylbenzoic acid methyl ester (19.2 g, 0.1 mol) and 30 ml ethanol were added, and heated to reflux, then hydronium (85%, 6 g, 0.1 mol) was dropped. The mixture was stirred at 353 K for 7 h under nitrogen. After finishing the reaction, the mixture was cooled to the room temperature, and dumped into ten folds of excess water to afford plenty of white solid, filtered and washed with water to yield 4-tert-butylbenzhydrazide (a) (15.6 g, yield = 81%). 4-Methyl benzoic acid (6.8 g, 0.1 mol)was added into a 50 ml three-neck flask, then heated to 313 K, and 10 ml (excessive) thionyl chloride was dropped slowly. The mixture was heated to 353 K, and refluxed for 7 h. After finishing the reaction, distilling residual thionyl chloride with rotary evaporator, getting slightly yellow liquid 4-methylbenzoyl To a 500 ml single-neck flask, 15.6 g (0.08 mol, excessive) (a), 250 ml tetrahydrofuran, 7.7 g (0.05 mol) (b) and 1 ml pyridine were added. The mixture was refluxed for 12 h. After finishing the reaction, the residual tetrahydrofuran was distilled and the mixture was precipitated into ice-water, filtered and washed with water to afford white solid. The crude product was recrystallized with ethanol three times to yield white sheet crystal (c) (13.4 g, yield 84%). A mixture of (c) (13.4 g, 42.2 mmol) and POCl 3 (250 ml) was stirred at 378 K for about 10 h, then poured into ice-water to yield slightly yellow crystals. The mixture was recrystallized with ethanol three times to afford colourless prisms of (I).

S2. Refinement
Positional parameters of all the H atoms were calculated geometrically and were allowed to ride on the C atoms to which they are bonded, with U iso (H) = 1.2U eq (C).

Figure 1
The molecular structure of (I) with displacement ellipsoids drawn at the 30% probability level (H atoms have been omitted for clarity).  The packing of (I).

Figure 3
The formation of (I). Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 )
x y z U iso */U eq N1 0.3647 (