2016年12月14日 · In the resonance structures of pyrrole, all carbons can formally bear a negative charge, so it's not immediately obvious which one is most electron-rich: My book claims that because resonance forms 1c and 1d are greater contributors to the resonance hybrid than 1b and 1e , the α-carbons (which bear the negative formal charge in 1c and 1d ) are ...

2020年8月1日 · Now, the preference of $2$-position in case of Pyrrole can be justified easily by considering the greater stability of the $\sigma$-complex intermidiate formed in case of substitution at $2$-position due to more number of resonating structures as clearly been described in the answer to the question Regioselectivity in Electrophilic Substitution ...

2017年2月27日 · $\begingroup$ "Remember, resonance is just a model." - +1 for this. More explicitly: we use resonance to deal with the limitations of using Lewis structures to represent molecules that exhibit electron delocalization. $\endgroup$ –

2017年10月1日 · The following figure shows the resonance structures we can draw to describe the intermediates produced by electrophilic at the 2- ($\alpha$) or 3- ($\beta$) positions in pyrrole. image source. You can see that the intermediate produced by attack at the $\alpha$-position can be described by 3 resonance structures.

$\begingroup$ Yes - it isn't resonance stabilised, and 23 is sort of normal, what are you comparing it against? The pyrrole anion has the lone pair in an sp2 orbital which makes it slightly more acidic than a typical sp3-hybridised amine. For comparison you can look at the "amides and carbamates" section in the Evans pKa table.

2018年3月2日 · That said, every resonating structure (except the uncharged one) for pyrrole and furan will create a formal positive charge on the hetero-atom. Since N is less electronegative than O, it will be slightly more stable than O with that positive charge. Hence, pyrrole will be more aromatic than furan.

2017年3月5日 · instead of drawing all 8 resonance structures for tropolone, we usually represent them by just drawing the one resonance structure shown at the bottom of the tropolone figure. and here are the resonance structures for furan. and for thiophene, they are the same as furan, just replace the oxygen with a sulfur atom in the resonance structures.

2020年5月3日 · Therefore, both structures of each pair have same stability equally favored. (g) Positive charge on $2^\circ$-$\ce{C}$ in both structures: Since positive charge is on a $2^\circ$-$\ce{C}$ of each compound, the relative energy due to carbocation is same on both structures. Yet, the first structure has its double bond conjugated to the carbonyl ...

2014年2月9日 · The Reimer-Tiemann reaction is known as the ortho-formylation of phenols under strongly alkaline conditions.. It's not an addition of a carbene to a double bond, like the Simmons-Smith reaction, the pyrrole to pyridine ring enlargement or the Buchner expansion, which is catalyzed by transition metals.

2020年8月25日 · However, in aniline, there is a partial loss of the lone pair due to resonance but the lone pair of nitrogen is still available for protonation. Aromaticity is not lost in the resonance structures of aniline. Therefore aniline is more basic than pyrrole but is less basic compared to pyridine (where the lone pair is out of plane of resonance).