Which Of These Drawings Represent Molecules?

Construction of Organic Molecules

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Here you lot volition learn how to understand, write, draw, and talk-the-talk of organic molecules. Why were dissimilar drawing techniques developed? Organic molecules can get complicated and large. It is a tedious to take to constantly draw out every particular, especially when not necessary, so the o-chemist of the by developed these techniques to make it more convenient and piece of cake. In add-on, some of these shorthand means of drawing molecules give us insight into the bond angles, relative positions of atoms in the molecule, and some eliminate the numerous hydrogens that can get in the way of looking at the backbone of the construction.

Introduction

Discover the following drawings of the structure of Retinol, the nigh common form of vitamin A. The first drawing follows the direct-line (a.k.a. Kekul é ) construction which is helpful when you desire to look at every single atom; nonetheless, showing all of the hydrogen atoms makes information technology difficult to compare the overall structure with other similar molecules and makes it difficult to focus in on the double bonds and OH group.

Retinol: Kekul é directly-line cartoon

The following is a bond-line (a.k.a. zig-zag) formula for retinol. With this simiplified representation, one can hands see the carbon-carbon bonds, double bonds, OH group, and CH₃ groups sticking off of the the main ring and chain. Besides, information technology is much quicker to draw this than the one above. Yous will larn to capeesh this type of formula writing after drawing a countless number of organic molecules.

Retinol: Bail-line or zig-zag formula

Importance of Construction

Learning and practicing the basics of Organic Chemical science will aid you immensely in the long run as you learn new concepts and reactions. Some people say that Organic Chemistry is similar another linguistic communication, and in some aspects, it is. At get-go it may seem difficult or overwhelming, just the more you lot practice looking at and cartoon organic molecules, the more familiar you will become with the structures and formulas. Another skilful idea is to get a model kit and physically brand the molecules that you have problem picturing in your head.

Through full general chemical science, you may have already experienced looking at molecular structure. The unlike ways to draw organic molecules include Keku l é (straight-line), Condensed Formul every bit, and Bond-Line Formulas (zig-zag). It will be more than helpful if you become comfortable going from one style of drawing to another, and look at drawings and agreement what they mean, than knowing which kind of drawing is named what.

An example of a cartoon that incorporates all three ways to draw organic molecules would be the post-obit additional drawing of Retin ol. The bulk of the drawing is Bond-line (zig-zag) formula, but the -CH₃ are written as condensed formulas, and the -OH group is written in Kekul é form.

A widely used way of showing the 3D construction of molecules is the use of dashes, wedges, and straight lines. This drawing method is essential because the placement of dissimilar atoms could yield different molecules even if the molecular formulas were exactly the same. Below are two drawings of a 4-carbon molecule with ii chlorines and two bromines fastened.

4-carbon molecule with 2 chlorines and two bromines 4-carbon molecule with two chlorines and 2 bromines

Both drawings look like they stand for the aforementioned molecule; even so, if we add together dashes and wedged we will see that two different molecules could exist depicted:

The two molecules in a higher place are unlike, evidence this to yourself by building a model. An easier way to compare the two molecules is to rotate i of the bonds (here, it is the bail on the right):

Notice how the molecule on the correct has both bromines on the aforementioned side and chlorines on the same side, whereas the first molecule is unlike. Read about Dashed-Wedged Line structures, bottom of page, to understand what has been introduced in a higher place. You will acquire more than about the importance of atomic connectivity in molecules every bit you go along on to larn near Stereochemistry.

Cartoon the Structure of Organic Molecules

Although larger molecules may look complicated, they tin can be easily understood by breaking them down and looking at their smaller components.

All atoms want to have their valence trounce full, a "closed shell." Hydrogen wants to have two due east^- whereas carbon, oxygen, and nitrogen want to have 8 e^-. When looking at the different representations of molecules, go along in mind the Octet Rule. Also call back that hydrogen tin bail 1 time, oxygen can bond up to 2 times, nitrogen can bond up to iii times, and carbon tin can bail up to iv times.

Kekulé (a.k.a. Straight-Line Structures)

Kekul é structures are similar to Lewis Structures, just instead of covalent bonds being represented by electron dots, the ii shared electrons are shown by a line.

(A) (B)(C)

Lone pairs remain every bit ii electron dots, or are sometimes left out even though they are nonetheless in that location. Notice how the three lonely pairs of electrons were not depict in around chlorine in example B.

Condensed Formulas

A condensed formula is made up of the elemental symbols. The guild of the atoms suggests the connectivity. Condensed formulas can be read from either management and H₃C is the same as CH₃, although the latter is more common considering Look at the examples below and match them with their identical molecule under Kekul é structures and bond-line formulas.

(A) CH₃CH₂OH (B) ClCH₂CH_twoCH(OCH₃)CH₃ (C) H₃CNHCH₂COOH

Let's look closely at example B. Every bit you go through a condensed formula, you want to focus on the carbons and other elements that aren't hydrogen. The hydrogen's are of import, but are usually in that location to consummate octets. Also, notice the -OCH₃ is in written in parentheses which tell you that it non part of the main chain of carbons. As you read through a a condensed formula, if you reach an atom that doesn't have a consummate octet by the time yous reach the next hydrogen, so it's possible that at that place are double or triple bonds. In instance C, the carbon is double bonded to oxygen and single bonded to another oxygen. Find how COOH means C(=O)-O-H instead of CH₃-C-O-O-H because carbon does not have a complete octet and oxygens.

Bond-Line (a.k.a. zig-zag) Formulas

The proper name gives away how this formula works. This formula is full of bonds and lines, and because of the typical (more stable) bonds that atoms tend to make in molecules, they often end upwardly looking like zig-zag lines. If you work with a molecular model kit yous will find information technology difficult to make stick straight molecules (unless they contain sp triple bonds) whereas zig-zag molecules and bonds are much more feasible.

(A) (B) (C)

These molecules correspond to the exact aforementioned molecules depicted for Kekul é structures and condensed formulas. Notice how the carbons are no longer fatigued in and are replaced by the ends and bends of a lines. In addition, the hydrogens accept been omitted, merely could be easily fatigued in (see practice problems). Although nosotros practice not unremarkably draw in the H'southward that are bonded to carbon, we do draw them in if they are connected to other atoms besides carbon (instance is the OH grouping above in example A) . This is done because it is not ever clear if the non-carbon atom is surrounded by lone pairs or hydrogens. Too in instance A, notice how the OH is fatigued with a bail to the second carbon, but it does not mean that there is a third carbon at the end of that bond/ line.

Dashed-Wedged Line Structure

As you may have guessed, the Dashed-Wedged Line structure is all about lines, dashes, and wedges. At start information technology may seem confusing, but with practice, understanding dash-wedged line structures volition become like second nature. The post-obit are examples of each, and how they can be used together.

In a higher place are 4-carbon chains with attached OH groups or Cl and Br atoms. Remember that each line represents a bond and that the carbons and hydrogens have been omitted. When you expect at or draw these structures, the straight lines illustrate atoms and bonds that are in the same airplane, the plane of the paper (in this instance, reckoner screen). Dashed lines show atoms and bonds that go into the folio, backside the plane, away from you lot. In the higher up case, the OH group is going into the airplane, while at the same fourth dimension a hydrogen comes out (wedged).

Blue dewdrop= OH group; White bead=H

Wedged lines illustrate bonds and atoms that come out of the page, in forepart of the aeroplane, toward you. In the 2d diagram to a higher place, the OH group is coming out of the airplane of the paper, while a hydrogen goes in (dashed).

Blue bead= OH group; White bead=H

As stated before, straight lines illustrate atoms and bonds that are in the aforementioned plane equally the newspaper, but in the 2nd example, the direct line bond for OH means that it it unsure or irrelevant whether OH is going away or toward you. It is too assumed that hydrogen is too connected to the aforementioned carbon that OH is on.

Blue bead= OH grouping; H is not shown

Attempt using your model kit to encounter that the OH grouping cannot lie in the same aeroplane at the carbon chain (don't forget your hydrogens!). In the final 2Dexample, both dashed and wedged lines are used because the attached atoms are not hydrogens (although dashed and wedged lines tin be used for hydrogens).The chlorine is coming out the page while bromine is going into the page.

Bluish bead=Cl; Red bead=Br

References

1. Vollhardt, Grand. Peter C., and Neil E. Schore. Organic Chemistry: Construction and Role. fifth ed. New York: W. H. Freeman Company, 2007. 38-40.
2. Klein, David R. Organic Chemistry I Equally a Second Linguistic communication. 2nd ed. Hoboken, NJ: John Wiley & Sons, Inc, 2007. 1-14.

Contributors

• Choo, Ezen (2009, UCD '11)

Which Of These Drawings Represent Molecules?,

Source: https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_%28Organic_Chemistry%29/Fundamentals/Structure_of_Organic_Molecules

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