Ethers, as we know, belong to a group of organic compounds having the formula R-O-R’, where the R and R’ denote the alkyl radicals. Dimethyl ether, also known as methoxymethane, is a colorless gas-bearing a faint odor. It has a molar mass of 46.07 g/mol and a density of 2.1146 kg/m3 as a gas at 00 C. In liquid form, it is volatile and poisonous. CH3OCH3 has its use as propellants in aerosol products like hair sprays. It is a low-temperature solvent and can also be used as adhesives and binding agents. Other than this, it has applications in varied areas like oxygen-blown gasifiers, welding and soldering industries, diesel engines, printing, and polymerization. Majorly dimethyl ether is manufactured via dehydration of methanol and the reaction goes as below: 2CH3OH ——-> CH3OCH3 + H2O (CH3)2O is highly flammable in nature and hence can pose danger. Also, it can cause eye irritation, blurring of vision, and anesthesia. Let us now proceed to have an elaborate discussion on the nature of chemical bonding inside a molecule of methoxymethane.
CH3OCH3 Lewis Structure
Lewis Structure is the initial step towards finding out about the chemical bonding in a given molecule. It deals with the valence or the outermost shell electrons which come together in pairs and form covalent bonds between atomic elements. We use electron dot notations to represent the valence electrons during the sketch of Lewis Structure. Let us calculate the total number of valence electrons in a (CH3)2O molecule: If we look into the periodic table, we can check that Carbon has a valency of 4, Oxygen has a valency of 6, and Hydrogen has only 1 valence electron. Total number of valence electrons in CH3OCH3 = 4 + 31 + 6 + 4 + 31 = 20. A molecule of dimethyl ether has 20 valence electrons. We need to find out the central atom of the given molecule. In organic chemistry, one of the most important key points to keep in mind while sketching the electron dot structure is that hydrogen atoms will usually take the terminal positions irrespective of the comparison in the electronegativity values. When we are drawing a CH3OCH3 molecule, we must remember that it consists of the ether (R-O-R’, here R=R’) group. So, the skeletal formula for dimethyl ether looks like this:
We can see that oxygen has acted as the central atom in this molecule flanked by two methyl groups at both sides. This is an exception to the general rule of always keeping the most electropositive element in the center while drawing the Lewis Structure. Here, Oxygen with the highest electronegativity value has taken the central position. We will now put the electron dot notations surrounding the atoms in the diagram: In the beginning, we have put electron pairs between two atoms be it C and H or C and O so that bond formation can take place. We have utilized 16 of our valence electrons to form 6 C-H and 2 C-O bonds. So, where shall we put the remaining four? Here comes the octet rule: The elements present in group 1 to group 17 of the periodic table show a tendency to achieve octet valence shell configuration of the noble gas elements like Ne, Ar, and so on. Exception: Hydrogen tends to achieve 2 electrons in its outermost shell to fulfill the He configuration. This is known as the octet fulfillment rule. If we check the elements in the dimethyl ether molecule, we find that all the hydrogen and carbon atoms have achieved their corresponding required configurations. However, oxygen only has four valence electrons surrounding it.
We have fulfilled the octet rule and used all the 20 valence electrons. Now, we have to check the formal charge values for these atoms inside the molecule. Formal Charge is calculated as:
In methoxymethane, Formal Charge of each C atom = 4 – 0.58 – 0 = 0. Formal Charge of each H atom = 1 – 0.52 – 0 = 0. Formal charge of the O atom = 6 – 0.5*4 – 4 = 0. All the nine atoms in the molecule are in their least possible formal charge values. Therefore, we have got our required Lewis Structure diagram:
CH3OCH3 Molecular Geometry
Let us now discuss how we can proceed further and understand the inside of the molecule in a better and clearer manner. We now already know how a 2-dimensional methoxymethane molecule looks like. We know about the valence electrons and the type of bonds formed (six C-H bonds and 2 C-O bonds). What we need to learn now is how this molecule appears in 3-dimensional space. For this, we have to know what the VSEPR model is. VSEPR stands for Valence Shell Electron Pair Repulsion theory. This theory is required to predict the molecular shape of several compounds although it has its own limitations. According to VSEPR theory, electrons being like-charged tend to experience repulsion amongst themselves in their negatively charged atmosphere. This repulsion needs to be minimized and hence atoms tend to stay apart from each other in order to maintain the stability of the molecule. These electrons form groups ( the lone pairs and the bonded pairs) and we consider the central atom only in VSEPR theory for ease of calculation. In VSEPR theory, we deal with AXnEx notations where: ‘A’ stands for the central atom, here we have the oxygen to be the central atom ‘X’ stands for the surrounding atoms, therefore the value of ‘n’ is 2 ( if we consider the C atoms or the CH3 groups) ‘E’ stands for the lone pairs on the central atom, ‘x’= 2. So, we have the AX2E2 notation for the methoxymethane molecule.
As we can see, we get a bent molecular geometry like water here. The bond angle of C-O-C is around 110 degrees due to methyl groups that experience steric repulsion. The electron geometry is tetrahedral. And, given below is the 3D image of the shape of the CH3OCH3 molecule.
CH3OCH3 Hybridization
Orbital hybridization is the next concept that we are going to talk about in this article. If we look at organic compounds like CH3OCH3, we have covalent bonds formed between carbon and hydrogen and also carbon and oxygen. If we want to explain this phenomenon of bond formation, we need to take the help of a model. Here we use the hybridization model. Orbital hybridization refers to the combination and mixing of atomic orbitals to form hybrid orbitals. The atomic orbitals must be of the same atom and bear equivalent energies. Let us look at our central atom in dimethyl ether molecule. It is Oxygen. Oxygen forms two single bonds with two Carbon atoms at its sides. Always remember, single bond refers to sigma pairing i.e. head-on-head overlap of orbitals. For this to happen, the s and the three p orbitals of Oxygen need to form sp3 hybridized orbitals. Also, if we check the coordination number of oxygen in this molecule, the value comes to 4 owing to the two bonded and the two lone or unshared pairs of valence electrons. Either way, we can conclude that the oxygen atom has sp3 hybridization.
CH3OCH3 Polarity
What do we mean by Polarity? Polarity is the concept or topic in chemistry where we talk about charge distribution inside a molecule of a compound. We know that dipole moment is used to measure electronegativity that is defined to be the degree to which any atomic element can attain electrons. When two elements forming a bond have a certain degree of difference in their electronegativity values (usually above 0.4), we get charges at the two poles making the bond polar in nature. Let us have a look at the Pauling electronegativity chart: The electronegativity value of C is 2.55, H is 2.20 and O is 3.44 as per the chart. The difference between C and H values is not quite significant but when it comes to the 2 C-O bonds, we will have a partial 𝛅+ on C and a 𝛅- on O atom. The difference is around 0.89 which results in the formation of polar bonds. The dipole moments of these bonds point in the same direction which does not result in the cancellation of the dipole of the molecule as a whole. The dipole value of methoxymethane is 1.3 D. Hence, we can say that CH3OCH3 is slightly polar in nature.
Conclusion
In this article on Methoxymethane or Dimethyl ether, we have covered Lewis Structure, VSEPR theory for 3D molecular geometry, hybridization, and also the concept of polarity. Happy learning! Note: CH3OCH3: Name: Dimethyl ether (DME)/Methoxymethane Polarity: Polar ( dipole 1.3D) Hybridization: sp3 Molecular Geometry: Bent Isomer: Ethanol
