Draw a resonance structure of the guanine molecule shown here, which is part of the DNA structur

Draw a resonance structure of the guanine molecule shown...

Key Concepts

Aromaticity

Aromaticity is a property of cyclic, planar molecules with conjugated ?-electron systems that fulfill Huckel’s rule. This concept explains why certain ring systems, such as those found in many biological molecules, exhibit extraordinary stability due to the delocalization of electrons over the entire ring.

Purine Structure

Purine is a type of bicyclic aromatic heterocycle that forms the core of nucleobases in DNA and RNA. Its unique fused ring system allows for significant resonance stabilization, contributing to its reactivity and role in biological systems.

Resonance Structures

Resonance structures are multiple valid Lewis structures that collectively describe the distribution of electrons within a molecule. They highlight how electrons can be delocalized across different atoms or bonds, leading to a stabilization of the molecule that cannot be captured by a single static structure.

Electron Delocalization

Electron delocalization refers to the phenomenon where electrons, particularly in ? systems, are spread over several atoms. This sharing of electron density among multiple atoms increases molecular stability and is best illustrated through the depiction of resonance structures.

Transcript

00:01 So for this question, we are asked to draw a resonance structure of the molecule guanine.

00:10 So this is the structure that we are given.

00:15 And the points that intersect that don't have an atom written, those are just understood to be carbon.

00:24 And also, the lone pairs are not drawn in because those are going to be understood.

00:29 However, i'm going to add the lone pairs to the nitrogen to oxygen to help us draw a valid resonant structure.

00:42 So i'm just going to add hydrogen attached to it.

00:48 I'm going to add the lone pairs to these atoms to help us visualize what is happening.

00:59 So between two resonant structures, we have our double -sided arrow.

01:03 And we know when we draw the resonance structure that the position of the atoms will not change.

01:12 So we can draw the structure exactly the same way because the only thing that we are going to be changing is the position of the electrons and not the atoms themselves.

01:32 Okay.

01:39 So i will just draw them all in as single bonds until we figure out where we're moving these electrons.

01:46 So remember electrons that move for resonance structures can only be changed from pie bonds, which are double or triple bonds, and lone pairs.

01:59 So all of the single bonds we are not going to touch or mess with on this original structure.

02:07 So first let's look at the pie bonds and loan pairs that we can move around to create a resonance structure.

02:19 So we have this double bond over here.

02:25 However, if we move it over here or over here, we really don't have any extra loan pairs to fulfill the octet rule for this carbon.

02:38 So moving it around over there doesn't make sense.

02:41 So we're going to leave that double bond, just how it is.

02:47 And we're going to focus on this ring where we have lots of pie bonds and loan pairs to move around.

02:59 So what we're going to do is we're just going to just move around some electrons.

03:05 So if we move this double bond to over here, then this carbon will still have a full octet.

03:24 Right? so we'll draw over here.

03:29 This carbon still has if the octet rule is satisfied.

03:33 But now this carbon on the bottom does not, right? we only have three.

03:39 So we're going to move this double bond over here.

03:46 So let's try that.

03:48 All right.

03:48 So now these two carbons have the octet rule satisfied.

03:55 But now since we move that double bond over there, now this carbon only has three bonds.

04:08 So we need to move more electrons.

04:13 So let's move this double bond from the oxygen down there...

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