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Everyday Analogies to understand Aromaticity -
- Sílvia Simon, Jordi Poater, Miquel Duran, and Miquel Solà from the Institut de Química Computaciona i Catàlisi, Universitat de Girona presented on using everyday analogies to understand aromaticity. - They discussed Hückel's rule for aromaticity in monocyclic systems with planar symmetry and how it strictly applies to systems with 4n+2 electrons in the ring. - The presentation concluded that everyday analogies can help explain aromaticity if combined with visual tools, and concepts need ways for people to see, touch, and experience them.
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Everyday Analogies to understand Aromaticity -
- 1. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16 Sílvia Simon, Jordi Poater, Miquel Duran, and Miquel Solà -Institut de Química Computaciona i Catàlisis, Universitat de Girona -Càtedra de Cultura Científica i Comunicació Digital -Departament de Química Inorgànica i Orgànica and IQTCUB, Universitat de Barcelona - ICREA EVERYDAY ANALOGIES TO UNDERSTAND THE CONCEPT OF AROMATICITY
- 2. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16 Garcia-Borràs, M., Osuna, S., Swart, M., Luis, J. M. and Solà, M. (2013), Maximum Aromaticity as a Guiding Principle for the Most Suitable Hosting Cages in Endohedral Metallofullerenes. Angew. Chem. Int. Ed., 52: 9275–9278. doi:10.1002/anie.201303636
- 3. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16 What is Aromaticity? Bond?
- 4. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16 Afegir una imatge de la densitat tallada 2D … que no trobo fàcilment .. buscar.
- 5. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16
- 6. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16
- 7. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16 But, are all molecules with electrons in a ring aromatic?
- 8. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16 4n+2 Hückel’s rule 4n+2 Hückel’s rule strictly holds for monocyclic systems like benzene and cyclooctatetraene (annulenes with planar symmetry)
- 9. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16
- 10. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16
- 11. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16 Conclusions Everyday Analogies Helped by some “fancy” tool Need to be seen, touched, …
- 12. @SilviaSimonR @C4DUdG @IQCCUdG#SUNYCoilUPF 13-14/10/16 THANK YOU FOR YOUR ATTENTION
Editor's Notes
- #2 In chemistry there are many concepts which are very difficult to be explain. Sometiomes it is because their explanation invole mathematics or some abstraction. BVu may be the most difficult think is that they are not related to any everyday experiencie. An exemple is when we introduce entropy in thermodinamics. It is always much more difficult that talking about energy, that it is something that they can extrapolate to some “real” thing. In that presentacion we would like to talk a very succes research line in the group leaded by Prof. Solà, aromaticity.
- #3 When one talks aromaticity, they immedialty relate it to smell/fragancy. But it is no that aromatic compounds are not longer related to the aroma but to the extrastability that some compounds present. This is the case of benzene, wchih is more stable than the correponding trien.
- #4 In order to define aromaticity we need to start defing chemical bond. Ussually we need to draw a bond like a stick that link two balls. In order to be able to explain the electron delocalization related to aromaticity we need to introduce a different picture of the chemical bond. A more “real” one, defined using electron density. Now it is time to fine some analogies to explain electron density (since now for our students it was very easy to “see” the bond as a simple stick and balls). So at thant moment one need to find some everyday analogy. In that cas it can be related to a Citiy population (atoms) and the movement (traffic) between both cities.
- #5 In that map we have two large cities with different populations (and different surface at the same time). The population density will be different in both cities, being larger in Barcelona (atom F in the HF molecule). We have people (cars) traveloing from one to another city. So electron density will change along the way to BCN from GRN. But this is the way of bonding both cities. If we analyse the number of cars (electron density) that go from GRN to DCN we will see that theri density is changing. We can see from the picture that near the city center the traffic is larger (orange), and proportional to the city size. Therea people leaving from Girona going directly to BCN, but many other just stop in some village between both bid cities. In that sense, between both center there will be a point where the density of cars is the samllest one. This is very nice everyday experience to explain what about electron density!
- #6 But what about benzene? What makes benzene to be so stable. The round circulation around BCN (the two rondas, de dlat and litoral) are a good example expalinig thei phenomena. If there wold be only on roand going from noth/south Barcelona there will be a big amount of cars, as all of the need to go through it independently of where they need to go. When all points are connected with a round road it is much easier to circulate, so in some wuya the traffic gets stabilized.
- #7 So, aromaticity is due to the electron delocalization within a ring. So we need to have electrons to be eable to be delozalized, so the pi ones (forming the doble bond) are the ones delocalized. So, any molecules with pi electron confined within a ring will be aromatic, presenting extra stabilization? NO! They need to follow some rules.
- #8 So, aromaticity is due to the electron delocalization within a ring. So we need to have electrons to be eable to be delozalized, so the pi ones (forming the doble bond) are the ones delocalized. So, any molecules with pi electron confined within a ring will be aromatic, presenting extra stabilization? NO! They need to follow some rules.
- #9 The Hückel’s rule is the one that need to be fulfilled for planar cycloootatetraenes. Benzene with 6 electrons fulfills the rule whiel ciclybutadiene has only 4 electrons. At that point it is not easy to find out an everyday analogy to explain these rule (and many other phenomenas which are base on quantum chemistry). --- Schödinguer card (performing the job to understand the differences from classic to quantum world).
- #10 In order to explain the difference between both molecules MO can be introduced. They are the representation of a pair of electrons. (take two cards, with different color and explain the that al MO are build by two of them, with different color). From the occupation (number of electrons) we can see that ….. So we need somtimes to introduce more complexes where it is difficults to fins everyday experiences, but the use of some tool (cards) can help to make our students to remember them.
- #11 In order to explain the difference between both molecules MO can be introduced. They are the representation of a pair of electrons. (take two cards, with different color and explain the that al MO are build by two of them, with different color). From the occupation (number of electrons) we can see that ….. So we need somtimes to introduce more complexes where it is difficults to fins everyday experiences, but the use of some tool (cards) can help to make our students to remember them.
- #13 In chemistry there are many concepts which are very difficult to be explain. Sometiomes it is because their explanation invole mathematics or some abstraction. BVu may be the most difficult think is that they are not related to any everyday experiencie. An exemple is when we introduce entropy in thermodinamics. It is always much more difficult that talking about energy, that it is something that they can extrapolate to some “real” thing. In that presentacion we would like to talk a very succes research line in the group leaded by Prof. Solà, aromaticity.