Aligning benzene wrt. its centre, in chemfig

Question

Back again, with more questions. This time, I need to align a reaction scheme involving benzene. This is what I currently have:

\diagram[1.0]{
    \schemestart[0, 1.5, thick]
    \chemfig{**6(------)}
    \arrow{0}[,0]       % used for alignment
    \hspace{5mm} + \hspace{5mm}
    \chemfig{E}
    \arrow
    \arrow{0}[,0]
    \chemfig{**[60,-240]6(----(-[:135]H)(-[:45]E)--)(-[:30,,,,draw=none]+)}
    \schemestop
}

The \diagram simply sets up some spacing and centring, and doesn't really affect this. Using this example, I get this output:

Rather, what I want is to have the first benzene, the +, the E, the arrow, and the centre of the second benzene be in a single row. I've tried playing around with invisible arrows and such, and the example above lets me have the first 4 -- benzene 1, +, E and arrow aligned.

Thanks.

---

Edit

I have slightly more troubles, and since it's highly related I don't think it would be good to create an entirely new question.

Now I have this code:

\diagram[1.0]{
    \schemestart[0, 1.5, thick]
    \chemfig{**[60,-240]6(----(-[:135]H)(-[:45]E)--)(-[:30,,,,draw=none]+)}
    \arrow{0}[,0]
    \hspace{5mm} + \hspace{5mm}
    \chemfig{@{el}E}
    \arrow
    \schemestop
    \schemestart[0, 1.5, thick]
    \chemfig{**6(----(-[:90]E)--)}
    \schemestop
}

And I get this output:

Sadly, nothing is aligned now. I went with Guho's solution, but I couldn't get unbonpetit's solution to produce a satisfactory result either.

Also, I noticed that I can't actually find a way to get chemfig to use the centre of the atom as the anchor point, even when I start in the centre, and use phantom atoms and bonds like so:

\chemfig{\phantom{+}-[:90,,,,draw=none]([:270]**6((-[:90]E)------))}

It still somehow insists on misaligning things (the atom is anchored somewhere in the middle of the centre and the top edge, it seems)

Anyway, thanks for the continued help. Both answers worked for the basic case, so there's that.

Answer 1

Another approach:

\documentclass{article}
\usepackage{chemfig}
\begin{document}
\schemestart[0,1.5,thick]
    \chemfig{**6(------)}
    \arrow{0}[,0]
    \+
    \chemfig{E}
    \arrow(--.base west)
    \chemfig[yshift=\the\dimexpr-1.5em\relax]{**[60,-240]6(----(-[:135]H)(-[:45]E)--)(-[:30,,,,draw=none]+)}
\schemestop
\end{document}

EDIT Here is 3 solutions to align molecules properly:

\documentclass{article}
\usepackage{chemfig}
\begin{document}
Solution 1: invisible bond starting from middle of left bond (this midpoint becomes the baseline point)

\schemestart[0, 1.5, thick]
    \chemfig{(-[:90,-0.5,,,draw=none]){}**[60,-240]6([:30]----(-[:135]H)(-[:45]E)--)(-[:30,,,,draw=none]+)}
    \arrow(.base east--){0}[,0]
    \+{2em,2em,}
    \chemfig{@{el}E}
    \arrow(--.base west)
    \chemfig{(-[:90,-0.5,,,draw=none]){}**6([:30]----(-[:90]E)--)}
\schemestop
\medbreak

Solution 2: yshift the baseline anchor

\schemestart[0, 1.5, thick]
    \chemfig[baseline={([yshift=1.5em]current bounding box.base)}]{**[60,-240]6(----(-[:135]H)(-[:45]E)--)(-[:30,,,,draw=none]+)}
    \arrow(.base east--){0}[,0]
    \+{2em,2em,}
    \chemfig{@{el}E}
    \arrow(--.base west)
    \chemfig[baseline={([yshift=1.5em]current bounding box.base)}]{**6(----(-[:90]E)--)}
\schemestop
\medbreak

Solution 3: yshift molecule

\schemestart[0, 1.5, thick]
    \chemfig[yshift=-1.5em]{**[60,-240]6(----(-[:135]H)(-[:45]E)--)(-[:30,,,,draw=none]+)}
    \arrow(.base east--){0}[,0]
    \+{2em,2em,}
    \chemfig{@{el}E}
    \arrow(--.base west)
    \chemfig[yshift=-1.5em]{**6(----(-[:90]E)--)}
\schemestop
\end{document}

Answer 2

An easy way is to split up the schemes. Since the two rings are the same size and drawn from the same starting atom, the centers will be aligned. I've also made use of the \+ command:

\documentclass{article}
\usepackage{chemfig}

\begin{document}
    \schemestart[0, 1.5, thick]
    \chemfig{**6(------)}
    \arrow{0}[,0]% used for alignment
    \+{5mm,5mm}
    \chemfig{E}
    \arrow
    \schemestop
    \schemestart[0, 1.5, thick]
    \chemfig{**[60,-240]6(----(-[:135]H)(-[:45]E)--)(-[:30,,,,draw=none]+)}
    \schemestop
\end{document}

Note that the first + does not align vertically with the second + nor the arrow (use of + directly as in your MWE produces the same result). This can be fudged with the third argument of \+, which is the vertical shift (0.4 mm looked pretty good to me):

\documentclass{article}
\usepackage{chemfig}

\begin{document}
    \schemestart[0, 1.5, thick]
    \chemfig{**6(------)}
    \arrow{0}[,0]% used for alignment
    \+{5mm,5mm,0.4mm}
    \chemfig{E}
    \arrow
    \schemestop
    \schemestart[0, 1.5, thick]
    \chemfig{**[60,-240]6(----(-[:135]H)(-[:45]E)--)(-[:30,,,,draw=none]+)}
    \schemestop
\end{document}