The study of carbon-containing compounds and their...

The study of carbon-containing compounds and their properties is called organic chemistry. Besides carbon atoms, organic compounds also can contain hydrogen, oxygen, and nitrogen atoms (as well as other types of atoms). A common trait of simple organic compounds is to have Lewis structures where all atoms have a formal charge of zero. Consider the following incomplete Lewis structure for an organic compound called histidine (an amino acid), which is one of the building blocks of proteins found in our bodies: Draw a complete Lewis structure for histidine in which all atoms have a formal charge of zero. What should be the approximate bond angles about the carbon atom labeled 1 and the nitrogen atom labeled 2 ?

The study of carbon-containing compounds and their properties is called organic chemistry. Besides carbon atoms, organic compounds also can contain hydrogen, oxygen, and nitrogen atoms (as well as other types of atoms). A common trait of simple organic compounds is to have Lewis structures where all atoms have a formal charge of zero. Consider the following incomplete Lewis structure for an organic compound called histidine (an amino acid), which is one of the building blocks of proteins found in our bodies:
Draw a complete Lewis structure for histidine in which all atoms have a formal charge of zero. What should be the approximate bond angles about the carbon atom labeled 1 and the nitrogen atom labeled 2 ?

Key Concepts

Organic Chemistry

Organic chemistry is the branch of chemistry that studies carbon-containing compounds, including their structures, properties, and reactions. This field encompasses a vast array of substances from simple molecules to complex polymers and biomolecules.

Lewis Structures

Lewis structures are diagrams that depict the bonding between atoms in a molecule as well as the lone pairs of electrons that may exist. They help in predicting the arrangement of atoms and understanding the electron distribution in a molecule.

Formal Charge

Formal charge is a bookkeeping method used to assign charges to individual atoms in a molecule based on the assumption that electrons in a chemical bond are shared equally. It is useful for determining the most stable Lewis structure, often favoring structures where atoms have a formal charge of zero.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule which is determined by the repulsion between electron pairs, as described by the VSEPR theory. This geometry helps predict bond angles and molecular shape, which are vital for understanding reactivity and properties.

Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that are appropriate for the pairing of electrons to form chemical bonds. The type of hybridization (such as sp2 or sp3) influences the geometry of the molecule, and thereby the approximate bond angles observed around an atom.

Transcript

00:01 Problem 165 says to complete the lewis structure for the amino acid histidine and give the bond angles for the labeled atoms, this carbon here, and this nitrogen here.

00:12 So histidine is one of the few ringed amino acids, and it's important for a lot of secondary structure in different proteins.

00:25 So the structure given on your book is a bit of a shell of the actual structure of histidine.

00:35 And so what we need to do is complete the structure by adding lone pairs of electrons and double bonds where necessary to fill up the octets of each of the atoms involved.

00:47 So we can start here with this carbon at the top.

00:51 We know that carbon typically associates with four valence electrons in reds.

00:55 Now it only has three.

00:58 The same is true for the carbon beneath it.

01:02 The easiest way to solve the problem for both of these carbons is to draw a double bond here.

01:12 So moving over to this nitrogen, we know that nitrogen usually has five valence electrons, and here we've only got two.

01:20 We also have a shortage of electrons for this carbon here.

01:26 So to solve at least one of the valence electrons for both the nitrogen and the carbon, we can add a double bond between these two atoms.

01:36 And still missing two on this nitrogen, we can add a lone pair to bring us to the five that we need.

01:44 So now we have all five electrons necessary around the nitrogen, all four around this carbon.

01:54 And here on this nitrogen, we only have three.

01:58 So adding a long pair brings this up to the necessary.

02:01 Ceres 5.

02:03 This carbon already has is already making four bonds, so it has all of the electrons necessary, as does this carbon here.

02:17 Oops, i forgot something i'm going to dry.

02:21 Sorry about that.

02:24 So moving over to the left here, again we have a bit of a shortage on this nitrogen, three as opposed to five, so adding a lone pair of electrons solves that problem...

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