The following picture is from E. V. Anslyn Physical Organic Chemistry and shows constructing of MO of methyl using QMOT. MOs $\textbf{E'}$ and $\textbf{D'}$ are formed by mixing $\textbf{D}$ and $\textbf{E}$. I can't quite imagine how the mixing goes here.
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$\begingroup$ Can you imagine the mixing of s and p atomic orbitals into sp? It's pretty much the same. $\endgroup$ – Ivan Neretin Sep 28 '15 at 10:24
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$\begingroup$ Yes thank you, that would illustrate the polarized p lobes, right? But in the mixing that leads to E', the 3 1s obitals meet out of phase. Why the resulting orbitals have these 3 1s orbital in "brown phase" and are not cancelled? $\endgroup$ – wuschi Sep 28 '15 at 10:51