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Chapter 17 ORGO 2
Benzene and aromatic compounds
Question | Answer |
---|---|
What does it mean a conjugated system ? | The double bonds are separated by only one single bond |
What is the formula of the simplest aromatic hydrocarbon (or arene) and what is its name? | Benzene C6H6 |
How many degrees of unsaturation has Benzene ? | Benzene has 4 degrees of unsaturation, this is Highly unsaturated. |
To what kind of reaction benzene does not undergo ? | Benzene does not undergo addition. |
What are the Kekule structures ? | Kekule structures are rapidly equilibrating mixture of two compounds, each containing a six-membered ring. |
what does any structure for benzene must have ? | 1) 6 Member ring and 3 additional degrees of unsaturation. 2) Planar 3) All C-C bonds are equal in lenght. |
What is the hybridization and bond angle of each carbon atom in benzene ? | All C-C bonds are sp^2 hybridized, and trigonal planar with 120* |
Benzene reacts with nucleophiles or electrophiles ? | Benzene reacts with Electrophile due to the 6 delocalized electrons above the ring. |
What special H NMR characteristic does the Benzene group has ? | The absorption at 6.5-8.0 ppm |
What is the requirement for a molecule to be Ortho, meta or para | ortho has a -1,2- metra has a -1,3- para has a -1,4- substitute in the benzene ring |
What are Polycyclic aromatic hydrocarbonds ? | Compounds containing two or more benzene rings that share C-C bonds, also called PAHs. |
How do we know Benzene unusually stable? | The low heat of hydrogenation of benzene means that benzene is specially stable. |
What are the Criteria a compound must have in order to be classified as aromatic ? | The molecule has to cyclic, planar, completely conjugated and contain a particular number of pi electrons. |
What does it mean for a compound to be cyclic ? | Each p orbital must overlap with p orbitals on two adjacent atoms. |
What does it mean for a compound to be Planar ? | All adjacent p orbitals must be Aligned so that the pi electron density can be delocalized |
What does it mean for a compound to be conjugated ? | That it must have a p orbital on every atom on the ring |
What is Huckel's rule and formula ? | Hucler's rule refers to the number of pi electrons (not the number of atoms) in a particular ring 4n +2Pi (n=0,1,2..) = aromatic 4n +pi = antiaromatic |