Putting together fundamental concepts Flashcards
Is the following molecule conjugated?
Are there any other possible resonance structures?
If the molecule is conjugated, propose a viable electron pushing method and the total different possible resonance structures. Make sure to properly label any atom(s) with a positive or negative formal charge.
No, for pi electrons to be conjugated, they must have only one bond length between them. The third carbon on 1,4-pentadiene creates two isolated pi-electron systems that are NOT in conjugation with each other; therefore, there are not other possible resonance forms for this structure.
Is the following molecule conjugated?
Are there any other possible resonance structures?
If the molecule is conjugated, propose a viable electron pushing method and the total different possible resonance structures and the hybrid structure. Make sure to properly label any atom(s) with a positive or negative formal charge.
Yes, because there is one bond length between the lone pair and the pi-electrons of the double bonds, and one bond-length between the pi-electrons of the two double bonds.
The carbon with a lone pair is known as a carbanion, and has a -1 formal charge. Note there is a resonance structure that represent a carbanion for each carbon in this molecule.
Is the following molecule conjugated?
Are there any other possible resonance structures?
If the molecule is conjugated, propose a viable electron pushing method and the total different possible resonance structures and the hybrid structure. Make sure to properly label any atom(s) with a positive or negative formal charge.
Yes, because there is only one bond length between the sp3-electrons of the oxygen (lone pairs) and the π-electrons of the double bond, as well as one bond length between the π-electrons of the double bond and the positive charge of the carbocation.
Oxygen with one covalent bond and three lone pairs will always have a -1 charge. Becuase this system is cojugated, and there is charge separation, there will be a neutral resonance form.
What is the hybridization of the nitrogen in the following molecule?
This is an exception to the “group” method for determining hybridization
The nitrogen is actually sp2 hybridized. This is because its lone electron pair is in cojugation with the aromatic system. Becuase the lone pair electrons takes part in aromaticity, we can not count it as a group. Thus, the lone pair is in the p orbital.
What is the hybridization of the nitrogen in the following molecule?
This nitrogen is also sp2 hybridized (as is pyrrole), but the lone pair is located in the sp2 orbital (unlike pyrrole’s lone pair, located in the p orbital).
What is the hybridization of the nitrogen in the following molecule?
This is the structure for nicotine, which contains a pyrimidine group and pyrrolidine group. The pyrimidine nitrogen is sp2 hybridized and pyrrolidine nitrogen is sp3 hybridized. Because there is not other pi-electrons in the pyrrolidine group, counting the groups around the molecule is sufficient to determine its hybridization.
What is the formal charge of the nitrogen in the following compound?
The nitrogen has a formal charge of zero (three bonds and a lone pair on nitrogen fullfils its valence and neutralizes it)
What is the formal charge of the nitrogen in the following compound?
-1. A nitrogen atom with two covalent bonds and two lone pairs of electrons are always -1 (using the equation for formal charge).
What is the formal charge of the oxygen in the following compound?
+1. When oxyen has three bonds and a lone pair it will always be +1 (this also checks out when using the formal charge equation)
