QUIMICA ORGANICA HETEROCICLICA EPUB DOWNLOAD!
O estudo do mecanismo desta reação desempenhou um papel fundamental na formulação de alguns princípios básicos em físico-química orgânica, tais como. Quimica Organica Heterociclica y Polimeros. 4 likes. Book. : Química orgánica heterocíclica by Varios and a great selection of similar New, Used and Collectible Books available now at.
|Published:||25 February 2014|
|PDF File Size:||15.87 Mb|
|ePub File Size:||18.62 Mb|
The OH group is said to be ortho, para-directing towards electrophiles. No substitution occurs in either meta position.
quimica organica heterociclica We can understand this by looking at the curly arrow mechanisms or by look- ing at the molecular orbitals.
In Chapter 21 p. In phenol it is the ortho and para positions that are electron-rich and, of course, the oxygen itself. We could show this using curly arrows.
The curly arrows actually give an indication of the electron distribution in the HOMO of the mol- ecule.
Química Orgánica Heterocíclica by Francisco Lezcano on Prezi
The reason is that quimica organica heterociclica HOMO has large coefficients at every other atom, just as the allyl anion had large coefficients at its ends but not in the middle Chapter 7. The numbers are best in naming compounds but we need ortho and para to describe the relationship between substituents.
Phenol brominates in both ortho positions. In this molecule they happen to be positions 2 and 6 but in other molecules, where the Quimica organica heterociclica group is not on C1, they will have other numbers, but they will still be ortho to the OH group. Use whichever description suits the point you are making.
The benzyl anion is simpler because we do not have the added complication of the differences in electronegativities between the oxygen and carbon atoms. According to simple calculations, quimica organica heterociclica highest occupied molecular orbital HOMO for the benzyl anion is a nonbonding molecular orbital MO with the distribution like this.
Substituição Aromática Eletrofílica
Most of the electron density is on the benzylic carbon atom not in the ring, but there is also significant electron density on the ring carbon atoms in the ortho and para positions.
The distribution for phenol will be different because it is not an anion and the oxygen atom is more electronegative than carbon but the overall distribution will be as predicted by the curly arrows—most on the oxygen and on the ortho and para carbon atoms.
NMR can give us some confirmation of the electron distribution The 1H Quimica organica heterociclica shifts of phenol give us an indication of quimica organica heterociclica electron distribution in the p system.
The more electron density quimica organica heterociclica surrounds a nucleus, the more shielded it is and so the smaller the shift see p. All the shifts for the ring protons in phenol are less than those for benzene 7.
- Química heterocíclica (Book, ) 
- Quinica Organica, 6th Ed, Carey, Organic Chemistry - McGraw-Hill - Google Buku
- Química heterocíclica
- Bestselling Series
There is little difference between the ortho and the para positions: The shifts are smallest in the ortho and para positions so these are where there is greatest electron density and hence these are the sites quimica organica heterociclica electrophilic attack.
The shifts in the meta positions are not significantly different from those in benzene. The best sol- vent is the rather dangerously inflammable carbon disulfide CS2the sulfur analogue of CO2. Under these conditions, para bromophenol is formed in good yield as the main product, which is why we started the bromination of phenol in the para position.
The minor product is ortho bromophenol.
Química orgánica heterocíclica
Benzene is less reactive than phenol towards electrophiles To brominate phenol, all we had to do was to mix bromine and phenol—if we do this with benzene itself, nothing happens.
We therefore say quimica organica heterociclica, relative to benzene, the OH group in phenol activates the ring towards electrophilic attack.
The OH group is activating and ortho, para-directing.
Benzene will undergo electrophilic aromatic substitution as we have seen quimica organica heterociclica a variety of reactions with catalysis by strong protic acids or Lewis acids such as AlCl3. It is the donation of electrons on the oxygen into the aromatic ring that makes phenol so much more reactive than benzene towards electrophiles.
Other groups that can donate electrons also activate and direct ortho, para. It reacts faster than benzene with electrophiles.