Using the curved arrows as a guide to placing the electrons,...

Key Concepts

Formal Charges

Formal charges are used to determine the distribution of electrical charge within a molecule by comparing the number of valence electrons in an atom with the number it 'owns' in a specific Lewis structure. Proper assignment of formal charges is essential in determining the most stable resonance forms and ensuring that the overall charge on the molecule remains consistent.

Curved Arrow Notation

Curved arrow notation is a method used in organic chemistry to represent the movement of electrons during chemical reactions or when generating resonance forms. The arrow starts at a source of electrons, such as a lone pair or bond, and points toward where the electrons are intended to move. This notation helps track electron flow and understand how bonds and charges are rearranged.

Resonance Structures

Resonance structures are alternative Lewis structures for a molecule that depict different possible distributions of electrons, particularly in systems with delocalized electrons. They are used to represent the electron delocalization that cannot be captured by a single Lewis structure, indicating that the actual electronic structure is a blend, or hybrid, of these resonance forms.

Transcript

00:01 Hey guys, so in this question, we're asked to find resonance structures for each of these compounds, given the curved arrows that were given in the textbook.

00:11 So in part a, we have this compound, and we have this curved arrow right here, denoting that electrons from this triple bond are moving to this nitrogen here.

00:23 So remember, when we have a curved arrow with two arrowheads right here, that means a pair of electrons are moving as opposed to one.

00:34 So when we redraw this structure, we have our ch3 remains the same.

00:39 Our c is going to be here.

00:41 And instead of three bonds, we are going to have a double bond here instead, since the electrons are now moving to the nitrogen.

00:50 So we'll have two pairs of electrons.

00:57 Now that we have this, we just need to make sure we have.

01:00 Our formal formal charges.

01:03 So we are going to have a negative charge on the nitrogen.

01:10 Since nitrogen has five valence electrons, we're going to subtract the number of bonds we have, so it's two, and we're also going to subtract the number of lone pairs of electrons we have, so we have four electrons.

01:25 So that's five minus six, so that's a negative one.

01:29 And then on this carbon, we have four valence electrons, and then we're going to subtract the number of bonds.

01:36 So that's three bonds.

01:38 So that's four minus three.

01:39 So that's a positive one.

01:43 So remember when we do resident structures, we want to make sure that the net charge of our formal charges is the same for both structures.

01:51 So when we add these together, we get a net of zero, which is the same as what we started with.

01:57 Moving on to part b, we have this compound right here.

02:01 So we see that the one pair of electrons is moving to this carbon or to this bond right here to fill the octet of the middle carbon right here...

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