A branched absorption peak with medium intensity at (970+/-20) cm-1 appears only in the infrared spectra of methylsulfones. The below mentioned aromaticsulfones are chosen to reveal the specificity. Crystal and molecular parameters of CH3CONH-C6H4-SO2R (R=-CH3,-CH2CH2OH)-CH2CONH2, are determined by application of single crystal diffraction of X-ray through Nicolet R3M/E diffracometer. The existence of hyperconjugation and its natures in group-SO2CH3, confirmed by further analyses on the parameters, result in the specificity of IR absorption of the group, which is proved characteristic and can be used to identify methylsulfones. The first part describes the detection results, ascertains their crystal and molecular structures, and shows that the aromaticsulfone exists as cross linking multi-molecules when R=-CH2CONH2 or as double molecules when R=-CH2CH2OH because of H bonds. The second part covers analyses on their molecular structures. The analyses demonstrate the hyperconjugation between sigma SC and pi SC in group-SO2CH3. The sigma CH hyperconjugate with pi SO. The strength of hyperconjugated bond CH decreases and its length tends longer. Due to the effect, the bond SC is not a pure single bond sigma, but one which possesses a certain degree of a double bond. Its IR wave number, between those of sigma SC and pi SC, attributes to the medium branched peak at (970+/-20) cm-1. The peak branch reflects two groups of the most stable hyperconjugating conformational isomers. The hyperconjugation is weakened by the substitution of one non H group for one H atom in-SO2CH3 and if the non H group does not conjugate with pi SO, the absorption at (970+/-20) cm-1 disappears as a characteristic peak. The intensity of absorption at (970+/-20) cm-1 conforms to the intensity of hyperconjugation between pi SO and its adjacent sigma CH. The third part introduces syntheses of the products, crystal preparations and their detections through X-ray diffraction.