In the kaplan book, it talks about antiaromaticity. Huckel molecular orbital theory free online course. Download the pdf question papers free for off line practice and view the solutions online. You can find help on this channel related tohuckel rule in. Use these assessments to practice identifying aromatic compounds and understanding of huckels rule. The quantum mechanical basis for its formulation was first worked out by physical chemist erich huckel in 1931. Compounds with n 1 the most common examples have n 1. Spherical polar coordinates provide the most convenient description for this and related problems with spherical symmetry. The position of an arbitrary point r is described by three coordinates r. Physical chemistry microlectures covering the topics of an undergraduate physical chemistry course on quantum chemistry and spectroscopy. Huckels rules are a set of few rules to identify an aromatic compound as benzenec6h6. Huckel s rule for aromaticity in 1931, german chemist and physicist erich huckel proposed a theory to predict if a planar ring molecule. If we look at the frost circle and we look at the molecular orbitals, we can understand huckel s rule a little bit better visually. The specific rule is that if you have an \sp2\ conjugated system, the lone pair will be involved if it makes the system more stable.
Pdf aromaticity, antiaromaticity, homoaromaticity and the. This includes multiresonating systems, charged and heterocyclic aromatic compounds. Doering 1951, although several authors were using this form at around the same time. Aromaticity means cyclic planar conjugated and huckels rule for a stable pi system. The huckel method or huckel molecular orbital theory, proposed by erich huckel in 1930, is a very simple linear combination of atomic orbitals molecular orbitals method for the determination of energies of molecular orbitals of. After completing this section, you should be able to. Huckels rule is applied to all molecules which obeys the criteria of aromaticity in cyclopentadienyl anion there are two double bonds which contributes 4.
Huckel molecular orbital theory mit opencourseware free. Chemistry aromatic compounds and huckels rule youtube. Criteria for aromaticity 1 the molecule is cyclic a ring of atoms 2 the molecule is planar all atoms in. But actually it turns out that a lot of them dont even smell at. Organic chemistry ii chem 252 chapter 14 aromatic compounds. In 1931, german chemist and physicist erich huckel proposed a rule to determine if a planar ring molecule would have aromatic properties. Aromaticity tutorial for cyclic, charged and heterocyclic. Homework statement probably a really stupid question.
You can find help on this channel related tohuckel rule in chemistry huckels rule huckel rule. Content management system cms task management project portfolio management time tracking pdf education learning management systems learning experience platforms virtual classroom course authoring school administration student information systems. The chemists peter debye and erich huckel noticed that solutions that contain ionic solutes do not behave ideally even at very low concentrations. The compound must contain sp2 hybridised carbon atoms. So, while the concentration of the solutes is fundamental to the calculation of the dynamics of a solution, they theorized that an extra factor that they termed gamma is necessary to the calculation of the activity coefficients of the solution. The most essential criteria for the aromatic character is. Huckel s rules are a set of few rules to identify an aromatic compound as benzenec6h6.
The best structure is consistent with the electronegativity of the atoms e. The motion of a free particle on the surface of a sphere will involve components of angular momentum in threedimensional space. Pdf aromaticity, antiaromaticity, homoaromaticity and the huckel. For furan with two lone pairs on the oxygen atom, if we count electrons from the carbon atoms, we have 4 one per carbon. According to huckels rule these compounds should not exhibit aromatic character. Debye huckel onsager equation derivation pdf download. Benzene and aromaticity h h h h h h h h h h h h c 6h 6 2.
It gives a triangle with one double bond, 2 lone pairs at the tip, and a negative charge. Join indias leading elearning platform for smarter and faster exam preparation. The supporting quantum mechanics required for the formulation of this rule was solved first by the german physical chemist and physicist erich armand arthur joseph huckel in the year 1931. It is the theoretical basis for huckels rule for the aromaticity of. In organic chemistry, huckels rule estimates whether a planar ring molecule will have aromatic. Mar 11, 2009 huckels rule for aromaticity what is n. Because you know it clearly comes from the word aroma. Destabilized highly reactive relative to the corresponding openchain conjugated system. The molecular orbital picture of cyclobutadiene 17. Youtube to mp3 of aromatic compounds and huckels rule. A well known compound that fulfills the rule is benzene.
But these compounds are definitely aromatic benzenoid. Save as pdf benzene and other aromatic compounds what does aromatic really mean. So one would think maybe all of these compounds smell good, or smell bad, or dont smell at all. Huckels rule definition of huckels rule by medical dictionary. Huckels rule is used in order to estimate the aromatic qualities of any planar ringshaped molecule in the field of organic chemistry. Huckels rule for aromaticity 6 electrons aromatic heterocycles also can be aromatic. In 1931, erich huckel postulated that monocyclic single ring planar compounds that contained carbon atoms with unhybridized atomic p orbitals would possess a closed bond shell of delocalized. Cycloheptatriene although obeys huckels rule yet it is not aromatic. How do the huckel and baird rules fade away in annulenes.
The requirements for antiaromatic are 4n pi electrons. Huckel molecular orbital theory aims to be a simple, descriptive, and nonmathematical introduction to the huckel molecular orbital theory and its applications in organic chemistry, thus the more basic text found in the book. In order to be aromatic, a molecule must have a certain number of pi electrons electrons with pi bonds, or lone pairs within p orbitals within a closed loop of parallel, adjacent p orbitals. Calculations of properties of some smallring hydrocarbons and free radicals. Huckels rule is not valid for many compounds containing more than one ring. Complete delocalization of pie electrons should take place in the atom. Encyclopedia article about huckel rule by the free dictionary. Topics include the need for quantum theory, the classical wave equation, the principles of quantum mechanics, particle in a box, harmonic oscillator, rigid rotor, hydrogen atom, approximate methods, multielectron atoms, chemical. In organic chemistry, huckels rule estimates whether a planar ring molecule will have aromatic properties. Pdf aromaticity, antiaromaticity, homoaromaticity and. Definition of huckels rule in the medical dictionary by the free dictionary. Aromaticity in molecules with more than one ring page 3 rings together, note that the molecule has eight pi electrons within the closed loop, and conclude correctly that the molecule is antiaromatic. For example, pyrene and transbicalicene contain 16 conjugated electrons 8 bonds, and coronene contains 24 conjugated electrons 12 bonds. Huckel rule article about huckel rule by the free dictionary.
Presentation mode open print download current view. Aromaticity tutorial for cyclic, charged and heterocyclic aromatic compounds. Huckel arrived at this rule by performing molecular orbital calculations on cyclic systems containing x carbon atoms, and with each carbon atom supplying one pi electron. So, while the concentration of the solutes is fundamental to the calculation of the dynamics of a solution, they theorized that an extra factor that they termed gamma is necessary to the calculation of the activity coefficients of the.
So six pi electrons fits huckels rule, which is the second criterion, which says that the ring has to have 4n plus 2 pi electrons. Pdf in 1931, german chemist and physicist sir erich huckel proposed a theory to help determine if a. In order to be aromatic,a molecule must have a certain number of pi electrons within a closed loop of parallel, adjacent p orbitals. In huckels rule, the formula 4n+2 is an algebraic expression of the series 2, 6, 10, 14. Review the answer to part b above if youve forgotten how to treat fused ring cases. If we look at the frost circle and we look at the molecular orbitals, we can understand huckels rule a. Aromaticity in molecules with more than one ring page 2 b underlying question. Aug 07, 2014 all aromatic compounds follow huckels rule.