Small molecules with C=C double bonds, called monomers, can join with one another to form long chain molecules called polymers. Thus, acrylonitrile, H₂C=CHCN, polymerizes under appropriate conditions to give polyacrylonitrile, a common starting material for producing the carbon fibers used in composites. (a) Write electron-dot structures for acrylonitrile and polyacrylonitrile, and show how rearranging the electrons can lead to formation of the polymer.

Verified step by step guidance

1. 1. Start by drawing the electron-dot (Lewis) structure for acrylonitrile, H₂C=CHCN. Remember that each line represents a pair of shared electrons, and each dot represents a single unpaired electron. Carbon has 4 valence electrons, Hydrogen has 1, and Nitrogen has 5.
2. 2. In the Lewis structure of acrylonitrile, you will notice that the carbon atoms are connected by a double bond (C=C). This double bond is the key to polymerization. The double bond can break, allowing the carbon atoms to form new bonds with other molecules.
3. 3. Now, imagine many acrylonitrile molecules, each with its double bond broken. These molecules can connect end-to-end, with each carbon atom forming a single bond with the carbon atom of the next molecule. This forms a long chain, or polymer.
4. 4. Draw the Lewis structure for the polyacrylonitrile. It will look like a repeated unit of the acrylonitrile molecule, but with single bonds between the carbon atoms instead of double bonds.
5. 5. The process of breaking the double bonds and forming new single bonds is a rearrangement of electrons. This is how small molecules (monomers) like acrylonitrile can join together to form large molecules (polymers) like polyacrylonitrile.

Key Concepts

Electron-Dot Structures

Electron-dot structures, also known as Lewis structures, represent the valence electrons of atoms within a molecule. They illustrate how atoms are bonded together and can help visualize the arrangement of electrons, including lone pairs and bonding pairs. Understanding these structures is crucial for predicting molecular geometry and reactivity, particularly in the context of polymerization where the arrangement of electrons changes as monomers link together.

Polymerization

Polymerization is the chemical process through which monomers, small molecules with reactive functional groups, chemically bond to form a polymer, a large and complex molecule. This process can occur through various mechanisms, including addition polymerization, where double bonds in monomers are broken to create long chains. Recognizing the types of polymerization and the conditions required for these reactions is essential for understanding how materials like polyacrylonitrile are synthesized.

C=C Double Bonds

C=C double bonds are a type of covalent bond between two carbon atoms, consisting of one sigma bond and one pi bond. These bonds are significant in organic chemistry as they provide sites for chemical reactivity, particularly in polymerization reactions. The ability to break these double bonds and form new bonds with other monomers is a key feature that enables the transformation of small molecules into larger polymeric structures.