Alkene Stability Order

Alkene stability increases with hyperconjugation and steric relief. Order of substituted alkenes:

$$\mathrm{R_2C=CR_2} \gt \mathrm{R_2C=CHR} \gt \mathrm{trans\!-\!RHC=CHR} \gt \mathrm{R_2C=CH_2} \gt \mathrm{cis\!-\!RHC=CHR} \gt \mathrm{RHC=CH_2} \gt H_2C=CH_2$$

Reason: More alkyl substituents provide greater hyperconjugation; cis isomers are less stable due to steric strain.