Linear relationships of variations of crystalline c-parameters of orthorhombic, triclinic and monoclinic n-alkane structures as a function of n, the carbon atom number, are established by linear least square fitting the data taken from the literature and compared with the relationships previously determined. In particular, the results correspond well with the predictions of Nyburg and Potworowski for Pbcm orthorhombic structures: they allow the precise determination of the mean carbon-carbon distance projected onto the chain axis that is equal to 1.2724 Angstrom and the gap value of 3.1476 Angstrom between the end-methyl-group carbon atom planes of the two consecutive molecule layers.