Nova V2676 Oph is the first classical nova in which C2 has been detected during its early phase near the visual-brightness maximum in addition to CN. The presence of C2 and CN in the nova indicates that its atmosphere was enriched in carbon with C/O > 1. Furthermore, molecule formation in the early phase is likely to be associated with the dust formation that started ∼90 days after the discovery. We have obtained isotopic ratios of carbon and nitrogen for this nova, and they are consistent with model predictions. Based on the lightcurves and optical spectra of the nova, the inferred mass of the white-dwarf component of V2676 Oph is relatively small (∼0.6M⊙). The absence of strong [Ne II] emission at 12.8 μm and the relatively small ejected mass from V2676 Oph support this hypothesis. However, the mass of the white-dwarf component should be higher (>∼1.0M⊙) according to the observed isotopic ratios and theoretical predictions based on thermonuclear runaways.