Double connectors

Let us construct now a molecule that is made from the minimal number of H2C fragments. As shown in Scheme 3.7b, since H2C is a double connector, the minimal molecule will be constructed from two such fragments. Click and we make a C=C bond in the molecule H2C=CH2. This molecule is called ethylene, and like methane, it is also a gaseous material. From ethylene, we make thepoZymer polyethylene (those plastic bags that are so convenient to have but that pollute the earth). Ethylene is also a member of a family of molecules that possess C=C bonds, which are called by the common name alkene. 

Finally, in Scheme 3.9c, we are asked to make the minimal molecule from the fragments H2C and O. Since both are double connectors, we need only one of each, and click, we form H2C=0, with a C=0 bond. The molecule is called formaldehyde, and its solution in water is known by the nameformalin, which, due to its antibacterial action, is used to preserve tissues of animals and humans. Formaldehyde is also the smallest member of the family of molecules called aldehydes, wherein the C=0 bond is connected to at least one H fragment. 

Si02—The Power of Multiple Connectivity of Atoms We started with Si and O, which are quadruple and double connectors, respectively, and we proceeded to construct from them molecules. We showed that the multiple connectivities of the two atoms form a basis for generating many, many possible molecules. Initially, we made the simplest 0=Si=0 molecule and then gradually proceeded to the giant covalent molecule that makes the sand of the earth and the raw material for glass making. 

In Lecture 3, we constructed wood alcohol, methanol (Scheme 5.1b), which is the smallest member of and a representative of the family called alcohols. As shown in Scheme 5.2a, all the family members are characterized by an OH group bonded to a carbon, which in turn can be bonded to a variety of groups. The next simple alcohol in Scheme 5.2b is ethanol. Based on the fragments kit in Scheme 5.1a, ethanol is constructed by clicking together the single-connector H3C with the double-connector H2C and the single-connector HO. Unlike methanol, which causes liver problems, blindness, and other ailments when drunk, ethanol, which is the alcohol used in wine and in spirits, is not at all harmful when drunk in moderate quantities. Of course, you cannot drink pure ethanol, but in the concentration it appears in wines (12-15%),... 

In the next step in Scheme 5.6b, we unclick C—H bonds, and we represent these sites with the electrons participating in connectivity in red. It is seen that there is one single connector C5H5 fragment, three different double connectors C6H4, and a few triple connectors, quadruple connectors, and so on. We can go on up to the sextuple-connector Cg, which we encountered in Lecture 4. 

Using the double connector C=0 fragment, we can click it to two carbon-based single-connector fragments to form the family of ketones. Acetone is a ketone, and all ketones share the (C)2C=0 unit. 

Scheme 5.8b depicts a saturated fatty acid, called palmitic acid, which is represented in the implicit cartoon with a skeleton without explicit notation of the C and H atoms. The term saturated means that there are no double bonds in the chain, and as can be seen beneath the structure, the chain is constructed from a click of one singleconnector HgC to 14 double-connector H2C fragments. The dangling connectivity of the last CH2 is in turn clicked to a single-connector COOH fragment. Palmitic acid is the most common fatty acid found in mammals, plants, and microorganisms. Excess carbohydrates in the body are converted to palmitic acid, and as a result, it is a major body component. As we drew it, the chain of palmitic acid is extended in shape, and therefore the many molecules of the acid can pack nicely together and... 

Scheme 6.2b exemplifies the states of Nirvana for N and O versus the heavier family members P and S, respectively. It is seen that O is always a double connector, whereas S has the freedom of using more of its valence electrons for the purpose of connectivity. S can therefore assume a connectivity of 2 like O, but it can also assume a four-way coimectivity by utilizing two additional valence electrons or a six-way connectivity by utilizing all the valence electrons. Similarly, N is always a triple connector, while P can also be a five-way connector by utilizing all the five valence electrons. In other words, unlike N and O, which adhere to the octet rule and have fixed connectivities, P and S can have alternative states of connectivity by utilizing more of their valence electrons for creating electron-pair bonds. 

Thus, as seen in Scheme 6.3, since O is a double connector, it will require two single-connector fluorine atoms, and click, we obtain the molecule OF2 that obeys... 

The first such molecule is made from a beryllium atom (Be) and as many hydrogen atoms as needed. Since Be is a double-connector atom and each H is a single connector, then as shown in Scheme 7.1, the atoms click and generate the familiar molecule BeH2- What shape will BeH2 prefer In order to predict the shape, we simply count the number of pairs around the atoms. Since Be is surrounded by two pairs, the maximum distance between the pairs will be obtained when the molecule adopts a hnear shape with a bond angle of 180° as shown in Scheme 7.1a. 

Scheme 9.3b shows three 4e-binders that serve as double connectors. A typical one is a diamine molecule like H2N(CH2)2NH2 that uses its two amino centers to form two bonds to a TM. Chemists call such ligands bidentate, namely a ligand that has two teeth to bite on the transition metal. Another type of bidentate ligand is the one... 

Scheme 9.7 shows some of the applications of this concept by constructing new molecules made from the organic and TM complex fragments. Thus, taking the two single-connector fragments (CO)5Mn and CH3, we can form a new Mn—C bond and the new complex, (CO)5Mn-< H3, shown in Scheme 9.7a. Similarly, using the double connectors (CO)4Fe and CH2, we can form a new complex with a double...

N is a triple connector, while O is a double connector, and hence, NO will not have an even number of electrons. It will be a free radical. This is apparent from the following drawing ... 

Since H2C and HN are both double connectors, the resulting molecules are the following ... 

From F2C and 0, which are double connectors, we generate the double-bonded F2C=0 and F2C=CF2 molecules. From FC and N, which are triple connectors, we generate the triple-bonded F—C=N and F—CM2—F molecules. 

The first fragment in Scheme 4.13 is a single connector, while the other two are double connectors. Another fragment of interest, not explicitly shown in Scheme 4.13, is a triple connector. Clicking the connectivities, we can generate the following four molecules ... 

Be is a double connector and hence it forms BeCl2. But since the isolated BeCl2 molecule is electron deficient, it will aggregate by accepting lone pairs form the Cl atoms of another molecule. The two structures are illustrated below ... 

Fe(C0)4 is a double connector and is isolobal to CH2. In principle, it can form a molecule with Fe=Fe double bond, which is an analogue of ethylene. It can form a three-membered ring p5 e(CO)4]3, which is an analogue of the (CH2)3 ring. It can form, in principle, many other rings. 

---