In this contribution we analize the chemical and rotational properties of a sample of hot HB stars in the globular clusters M15 M79 M80 and NGC 2808 with effective temperatures Teff between 7000 K and 25000 K. To this purpose we have used high resolution spectroscopy with UVES+VLT. Our study reveals the existence of a discontinuity in the rotational rate distribution with temperature detected also by Behr et al. 1999 and 2000 in M13 and M15. Stars with Teff< 11000 K show a range of vsini values up to 30 km/s. All the stars with Teff > 11000 K however are slow rotators with vsini < 12 km/s. This discontinuity seems to coincide with the onset of diffusive processes in the stellar atmosphere which cause abundance anomalies in the hotter stars: overabundances of metals and helium depletion. This is confirmed also by the chemical analysis performed in 10 of the M79 targets in which we have found evidences of radiative levitation of metals and gravitational settling of helium for stars with temperatures hotter than 11000 K.