Hyperconjugation affects several properties.
# Bond length: Hyperconjugation is suggested as a key factor in shortening of sigma bonds (σ bonds). For example, the single C–C bonds in 1,3-butadiene and propyne are approximately 1.46 Å in length, much less than the value of around 1.54 Å found in saturated hydrocarbons. For butadiene, this can be explained as normal conjugation of the two alkenyl parts. But for propyne, it is generally accepted that this is due to hyperconjugation between the alkyl and alkynyl parts.
# Dipole moments: The large increase in dipole moment of 1,1,1-trichloroethane as compared with chloroform can be attributed to hyperconjugated structures.
# The heat of formation of molecules with hyperconjugation are greater than sum of their bond energies and the heats of hydrogenation per double bond are less than the heat of hydrogenation of ethylene.
# Stability of carbocations:
#:(CH)C > (CH)CH > (CH)CH > CH
#: The three C–H σ bonds of the methyl group(s) attached to the carbocation can undergo the stabilization interaction but only one of them can be aligned perfectly with the empty p-orbital, depending on the conformation of the carbon–carbon bond. Donation from the two misaligned C–H bonds is weaker. The more adjacent methyl groups there are, the larger hyperconjugation stabilization is because of the increased number of adjacent C–H bonds.