Recently, there has been a rapid development in the preparation of multiple bond systems with heavy main group elements phosphorus and carbon. Ab initio self-consistent field (SCF) molecular orbital calculations were performed at the 4-31G ∗ level to determine the effect of substituent groups -F, -CF 3, H-CC-, CH 2CH-, and phenyl, on the CP triple bond. A characteristic feature of phospha-alkynes is the weak sensitivity of the CP bond length to the substituent at the carbon atom. The molecular electrostatic potential analysis clearly reflects the strengths of the electronegativities of these substituent groups and their ability to attract the polarizable charge from the CP triple bond. The CP group deactivates the phenyl ring towards electrophilic attack.