Question #44162

Consider the following compounds at 298 K: (I) $N,N$-dimethyl-4-nitroaniline (II) $N,N$,2,6-tetramethyl-4-nitroaniline (III) $N,N$,3,5-tetramethyl-4-nitroaniline

Evaluate the following four statements regarding their electronic properties and structural features: \begin{itemize} \item[S1:] The observed dipole moment of (I) is substantially greater than the vector sum of the dipole moments of nitrobenzene and $N,N$-dimethylaniline due to synergistic $+M$ and $-M$ effects. \item[S2:] In compound (II), the $C_{ring}-N(CH_3)_2$ bond length is shorter than the corresponding bond in compound (I) due to the $+I$ effect of the ortho-methyl groups. \item[S3:] Compound (III) exhibits a lower dipole moment than compound (I) because steric B-strain forces the $-NO_2$ group out of coplanarity, disrupting the extended $\pi$-conjugation. \item[S4:] In compound (II), the $-N(CH_3)_2$ group exerts primarily a $-I$ effect on the benzene ring rather than a $+M$ effect, due to its orthogonal orientation relative to the $\pi$-system. \end{itemize}

How many of the above statements are correct?