A structural study of odd-numbered n-alkane (C n ) binary mixtures (C 2 1 : C 2 3 ) was carried out on powder samples using a Guinier-de Wolff camera with increasing concentration of n-C 2 3 at 293 K.Despite the reports in the literature, these molecular alloys do not form an orthorhombic continuous homogeneous solid solution to C 2 1 from C 2 3 at low temperature . Instead, as already observed in two even-numbered C n systems, X-ray diffraction results show the existence of seven solid solutions as the molar concentration of C 2 3 increases: four terminal solid solutions, denoted β 0 (C 2 1 )β 0 (C 2 3 ), isostructural with the low temperature phase of pure C 2 1 and C 2 3 (Pbcm), β 0 (C 2 1 ) and β 0 (C 2 3 ), identical to the phase β 0 which appears in pure C 2 3 above the δ transition, and three orthorhombic intermediate solid solutions, designated β 1 , β 1 and β 2 .On the basis of powder X-ray photographs, the phases β 1 and β 2 (C 2 1 : C 2 3 ) are indistinguishable, and they are isostructural with the intermediate solid solution β of the even-numbered C n binary systems (C 2 2 : C 2 4 ) and (C 2 4 : C 2 6 ). The phase β 1 (C 2 1 : C 2 3 ) is also isostructural with the two indistinguishable intermediate solid solutions β 1 and β 2 of the molecular alloys (C 2 2 : C 2 4 ) and (C 2 4 : C 2 6 ).From this study and our other laboratory results, the sequences of appearance of the solid solutions and the structural identities between these phases are established at low temperature for all the binary molecular alloys of consecutive C n (odd-odd, even-even or odd-even: 19 < n < 27) when increasing the solute concentration.