For benzene, we find that n1, which is a positive integer, so the rule is met. In order to be aromatic,a molecule must have a certain number of pi electrons. 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. After completing this section, you should be able to. How do the huckel and baird rules fade away in annulenes. The supporting quantum mechanics required for the formulation of this rule was solved first by the german physical chemist and physicist erich. Pdf download the chemistry of organic silicon compounds vol. 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. The first rule implies that every diagonal element is. So, to give the overview of candidates here in this page, we have given the entire material. Huckels rule 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. The most essential criteria for the aromatic character is that the compound must obey huckels rule. 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.
His rule states four criteria, a molecule should follow in order to be aromatic 2. Debye huckel onsager equation derivation pdf download. The 8 carbon ring having 8 pielectrons would not show aromatic character. Working scholars bringing tuitionfree college to the community. The compound must contain sp2 hybridised carbon atoms. Huckels rule for aromaticity in 1931, german chemist and physicist erich huckel proposed a theory to predict if a planar ring molecule would be aromatic or not. Huckels rules are a set of few rules to identify an aromatic compound as benzenec6h6. Huckel molecular orbital theory mit opencourseware. Doering 1951, although several authors were using this form at around the same time. Huckels rule is a theory which helps to determine if a planar ring molecule is aromatic or not. Thus, the aromatic numbers are 2, 6, 10, and so on.
Benzene and aromaticity h h h h h h h h h h h h c 6h 6 2. Complete delocalization of pie electrons should take place in the atom. Aromatic compounds and huckels rule organic chemistry. Youtube to mp3 of aromatic compounds and huckels rule. In organic chemistry, huckels rule pertains to aromatic molecules, meaning. Save as pdf benzene and other aromatic compounds what does aromatic really mean.
Download the pdf question papers free for off line practice and view the solutions online. Free pdf download of ncert solutions for class 11 chemistry chapter hydrocarbons solved by expert teachers as per ncert cbse book guidelines. In benzene, each of the carbon atom is sp2 hybridised. If you have understood this concept not studying or watching you can get 46 marks in csir. The readings column refers to relevant sections in the course textbook, l. Aromaticity important topic for csirnet, gate, iitjam. There are some conditions for application of huckels rule. Huckel molecular orbital theory in general, the vast majority polyatomic molecules can be thought of as consisting of a collection of twoelectron bonds between pairs of atoms. So if n is equal to 1, huckels rule is satisfied because i would do 4 times 1 plus 2. If a different molecule has 8 pi electrons 4 conjugated double bonds, it will not follow huckels rule no matter what integer you designate n to be. Huckels rule is strictly for monocyclic aromatic compound, its application to polycyclic aromatic compounds is tenuous. Physical chemistry microlectures covering the topics of an undergraduate physical chemistry course on quantum chemistry and spectroscopy.
One of the most important among them is that the molecule must have a planar structure. Lecture handouts organic chemistry i chemistry mit. In organic chemistry, huckels rule estimates whether a planar ring molecule will have aromatic. Some lecture notes apply to multiple class sessions. Hydrocarbons questions with solutions to help you to revise complete syllabus and score more marks in your class 11 examinations. Aromaticity and huckels rule chemistry video edurev. So if we count the number pi electrons in benzene, we can see there are two, four, and six. This section contains notes used to supplement the lectures for the course.
May 08, 2020 aromaticity and huckels rule chemistry video edurev is made by best teachers of chemistry. Pdf aromaticity, antiaromaticity, homoaromaticity and the huckel. Download my free guide 10 secrets to acing organic chemistry here. These cyclic hydrocarbons with alternating double and single carbon carbon. Pdf aromaticity, antiaromaticity, homoaromaticity and. Pdf if you have any doubts or want notes on a read more. Aromatic compounds and huckels rule video dailymotion. Aromaticity important topic for csirnet, gate, iitjam, jee, neet. 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 bonding, nmr, and particle in. Since there are 6 pi electrons, it follows huckels rule because when n1 you obtain a value of six. Ncert solutions for class 11 chemistry chapter hydrocarbons. Students who are planning to start their preparation by checking the niper jee syllabus 2020 and niper joint entrance exam pattern 2020 can check it from this article. Every exam there is a question from aromaticity topic.
Compounds with n 1 the most common examples have n 1. A well known compound that fulfills the rule is benzene. The value of n can be any integer as long as you are able to equate the number of electrons in the pi orbital to the huckels rule. If we look at the frost circle, and we look at the molecular orbitals, we can understand huckels rule a little bit better visually. This video is highly rated by chemistry students and has been viewed 2366 times. According to huckels rule these compounds should not exhibit aromatic. These notes contain huckels rule of aromaticity and solve examples form different examination. Presentation mode open print download current view. Huckels rule is used in order to estimate the aromatic qualities of any planar ringshaped molecule in the field of organic chemistry. Aromatic compound an overview sciencedirect topics. It is a linearized poissonboltzmann model, which assumes an extremely simplified model of electrolyte solution but nevertheless gave accurate predictions of mean activity coefficients for ions in dilute solution.
633 878 1139 1132 799 1112 1573 1550 1225 1562 797 1159 1291 1438 464 575 854 634 1190 1038 1041 1012 586 743 1406 938 917 1485 281 1309 1168 457 1169 454 1032 401 857 482 1162 809 865 1252 733