Benzoic acid is a food preservative. The space-filling model for benzoic acid is shown below. Dr

Benzoic acid is a food preservative. The space-filling model...

Key Concepts

Lewis Structure

The Lewis structure is a diagram that represents the arrangement of atoms in a molecule and shows all valence electrons explicitly, including bonds (as shared pairs) and lone pairs. It serves as a fundamental tool in organic chemistry to illustrate how atoms are connected in a molecule, providing insights into overall shape, bonding, and potential reactivity.

Resonance Structures

Resonance structures are multiple valid Lewis structures for a single molecule that depict the delocalization of electrons beyond a single, fixed arrangement. Instead of a single structure, resonance acknowledges that the true electron distribution is a hybrid of all possible representative forms, which is crucial for understanding stability and reactivity in molecules like benzoic acid.

Functional Groups (Carboxylic Acid)

The carboxylic acid functional group, typically represented as COOH, is a key component in benzoic acid. This group consists of a carbonyl (C=O) and a hydroxyl (OH) group bonded to the same carbon, contributing acidic properties by readily donating a proton. Recognizing this group is essential for understanding chemical behavior such as acidity and reactivity in various environments.

Aromaticity

Aromaticity refers to the enhanced stability of a cyclic, planar molecule with a conjugated system that follows Huckel’s rule (having 4n+2 ? electrons). In benzoic acid, the benzene ring is aromatic, which not only contributes to the molecule’s stability but also influences reactivity and the distribution of electrons in the overall structure, particularly when considering resonance delocalization.

Transcript

00:02 So in this video, we're going to go over question 112 from chapter 8, which says benzoic acid is a food preservative.

00:09 The space filling model for benzodia acid is shown below.

00:12 Draw the lewish structure from benzoic acid, including all resonant structures in which all atoms have a formal charge of zero.

00:20 So let's take a look at the space filling model.

00:23 So here's your space filling model, and in this model, the black atoms are carbon atoms, and the tiny blue atoms are hydrogen atoms, and the red atoms are oxygen atoms.

00:33 So what it looks like is it looks like we have a six -membered ring of carbon atoms, five of which have hydrogen atoms bonded to them.

00:43 And then that six -membered ring is bonded to another carbon atom, which has two oxygen atoms on it, one of which has a hydrogen atom bonded to it.

00:52 So let's go ahead and draw that skeletal structure.

00:57 So for benzoic acid, i have my six -membered ring, and then five of my atoms in my six -membered ring.

01:03 Membered ring have a hydrogen atom bonded to them and then that six -membered ring is attached to another carbon atom which is attached to two oxygen atoms and one of those oxygen atoms has a hydrogen atom on it.

01:14 So now i have my skeletal structure.

01:18 So what kind of details do we want to fill in? well we want all of the atoms in this structure to have a formal charge of zero.

01:26 So since oxygen likes to have two likes to make two bonds that usually gives it a formal charge of zero, if it has two bonds and two lone pairs of electrons, then i'm going to take this carbon oxygen bond and make it a double bond and then fill in my octet here, and i'll go ahead and fill in the octet on my other oxygen atom as well.

01:48 Now the formal charge on both of the oxygen atoms is zero because we have four minus four electrons minus two bonds gives us zero.

01:57 Sorry, six minus four electrons minus two bonds gives us zero.

02:01 So the formal charge on my oxygen, atoms is zero.

02:04 What about my carbon atom? well, since carbon is making four bonds, i have four valence electrons minus zero electrons in lone pairs minus four bonds.

02:12 So i have a formal charge of zero here as well.

02:16 Unfortunately, i'm not so lucky with my atoms in the ring.

02:20 They do not have formal charges of zero.

02:22 As they're written right now, each of those carbon atoms is only making three bonds and has no lone pairs of electrons.

02:29 So the formal charge would be four minus three is plus one.

02:33 So instead, we want these carbon atoms to be making four bonds.

02:37 So i'm going to go ahead and introduce a double bond right here.

02:43 Now, these two carbon atoms are both making four bonds, and their formal charge is four minus four is zero.

02:49 But what about my other carbon atoms? so my other four carbon atoms in the ring don't have formal charges of zero, so we want to fix that...

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