Chapter 21 Flashcards
resonance energy is the difference in energy between a resonance hybrid and the … in which electron density is localized on particular atoms and bonds
most stable hypothetical contributing structure
(aromaticity reqs) the molecule must be … and there must be a … on each atom of the ring (there cannot be any … atoms in the ring)
cyclic; 2p orbital; sp3 hybridized
(aromaticity reqs) there must be … pi electrons in the aromatic pi system, where n is a positive integer
4n + 2
some hydrocarbons are considered antiaromatic, because they are much less stable (more reactive) than an acyclic analog with the same number of pi electrons. an antiaromatic hydrocarbon has … pi electrons
4n
antiaromatic hydrocarbons must also be .., have a … orbital on each atom of the ring, and be … to display full antiaromatic properties
cyclic; 2p; planar
to avoid antiaromaticity, larger potentially antiaromatic structures such as cyclooctatetraene adopt a … with alternating double and single bonds. as a result, two different C-C bond lengths are observed corresponding to single and double bonds
nonplanar geometry
To predict the pattern of molecular orbitals found on a molecular orbital energy diagram, it is helpful to use the … method (Frost circles).
inscribed polygon
an annulene is a planar, cyclic hydrocarbon that contains
continuously overlapping 2p orbitals
an annulene is named by adding the number of atoms int he ring in … in front of the word …
brackets; annulene
Because … ring systems can satisfy the Hückel criteria for aromaticity, they are highly stabilized compared to other nonaromatic …
charged; cations or anions
For benzene rings with two substituents, the three possible constitutional isomers are named ortho (…-substitution), meta (…-substitution), and para (…substitution),
1,2; 1,3; 1,4
When one of the substituents has a special name (e.g., if NH2 is present, the molecule is an aniline), the molecule is named after that … and the key group is assigned the number 1.
parent molecule
if none of the groups impart a special name, the substituents are listed in …. followed by the word …
alphabetical order; benzene
polynuclear aromatic hydrocarbons contain more than one benzene ring, each pair of which shares
two C atoms
phenols are more … than simple alcohols
acidic
