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Example Questions
Example Question #1 : Identifying Aromatic Compounds
Consider the structure of cyclobutadiene, shown below:
Is this molecule aromatic, non-aromatic, or antiaromatic?
Non-aromatic
Aromatic
It depends on the environment
Antiaromatic
Antiaromatic
An aromatic must follow four basic criteria: it must be a ring planar, have a continuous chain of unhybridized p orbitals (a series of sp2-hybridized atoms forming a conjugated system), and have an odd number of delocalized electron pairs in the system. If the molecule fails any of the first three criteria, it is considered non-aromatic, and if it fails the only the fourth criterion (it has an even number of delocalized electron pairs), the molecule is considered antiaromatic. In the case of cyclobutadiene, by virtue of its structure follows criteria and . However, it violates criterion by having two (an even number) of delocalized electron pairs. Although it's possible that a molecule can try to escape from being antiaromatic by contorting its 3D shape so it is not planar, cyclobutadiene is too small to do this effectively. Therefore, cyclobutadiene is considered antiaromatic.
Example Question #11 : Identifying Aromatic Compounds
Assuming that this molecule is planar, determine whether this molecule is aromatic, and name the number of electrons ( molecular orbitals).
Aromatic, 6 electrons
Not aromatic, 8 electrons
Aromatic, 8 electrons
Non aromatic, 6 electrons
Not aromatic, 8 electrons
There is no p orbital surrounding the Boron atom, so the ring does not have a fully conjugated pi system. In addition, there are 8 electrons, which does not follow Huckel's rule (an aromatic system contains 4n+2 electrons). The pi electrons include the lone pair (not shown, but implicit) on the nitrogen atom, which is why the answers with "6 electrons" are not correct.
Example Question #11 : Organic Functional Groups And Molecules
Assuming that this molecule is planar, determine whether this molecule is aromatic, and name the number of electrons (not molecular orbitals).
Not aromatic, 6 electrons.
Aromatic, 6 electrons.
Not aromatic, 8 electrons.
Aromatic, 8 electrons.
Aromatic, 6 electrons.
The lone pairs on the two nitrogen atoms reside in sp2 orbitals, meaning they do not participate in resonance. Within the ring, there are three bonds, meaning there are six electrons. Thus, the molecule is aromatic because it is planar and follows Huckel's rule.
Example Question #11 : Organic Functional Groups And Molecules
Identify the given organic functional group.
Aldehyde
Acid anhydride
Ketone
Ester
Carboxylic acid
Aldehyde
Aldehydes are carbonyls with one R-group and one hydrogen attached to the carbonyl carbon.
Example Question #1 : Identifying Carbonyl Compounds
Identify the given organic functional group.
Acetal
Aldehyde
Ester
Carboxylic acid
Ketone
Ketone
Ketones are carbonyls with two R-groups attached the the carbonyl carbon.
Example Question #1 : Identifying Carbonyl Compounds
Identify the given organic functional group.
Amide
Ester
Acid halide
Carboxylic acid
Acid anhydride
Acid halide
This is an acid halide, were X is any halogen (group VII). They are the most reactive of all the carboxylic acid derivatives.
Example Question #1 : Identifying Carbonyl Compounds
Identify the given organic functional group.
Carboxylic acid
Aldehyde
Ester
Ketone
Acid anhydride
Carboxylic acid
Carboxylic acids are composed of one R goup and a hydroxy group bound to the carbonyl carbon. The hydroxyl group gives the molecule acidic properties.
Example Question #2 : Identifying Carbonyl Compounds
Identify the given organic functional group.
Aldehyde
Ester
Acid anhydride
Hemiketal
Acetal
Hemiketal
This is a hemiketal. Hemiketals are formed from the reaction of a ketone with an alcohol. The alcohol attacks the carbonyl carbon, reducing the double bond and adding a hydroxyl group.
Example Question #3 : Identifying Carbonyl Compounds
Identify the given organic functional group.
Ketal
Hemiacetal
Acetal
Acid anhydride
Hemiketal
Ketal
Ketals have two -OR groups bound to a central carbon. The R groups attached to the oxygens are not necessarily the same. Ketals result from the reaction of a ketone with two equivalents of alcohol.
Example Question #1 : Identifying Carbonyl Compounds
Identify the given organic functional group.
Ester
Hemiacetal
Acetal
Carboxylic acid
Acid anhydride
Acid anhydride
Acid anhydrides are relatively reactive, since they have a fairly good leaving group (the conjugate base of a carboxylic acid) [COO-]. They are formed by reacting two carboxylic acids via dehydration synthesis.
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