How To Draw Molecules Given A Formula

Affiliate 10. Organic Chemistry

10.1 Condensed Structure and Line Structure

Learning Objectives

By the cease of this department, you volition be able to:

Interpret condense and line structures.
Draw the condensed construction of a given Lewis Construction or line structure.
Draw the line structure of a given Lewis Structure or condense structure.

If you wait ahead in this chapter and in other resource at the fashion organic compounds are drawn, you will see that the figures are somewhat dissimilar from the Lewis structures y'all are used to seeing in your full general chemistry book. In some sources, you will see condensed structuresfor smaller molecules instead of full Lewis structures:

**Figure i.** Comparing betwixt Lewis structures and condensed structures.

Case 1

Make up one's mind the Lewis Structure of the following condensed structure of oleic acid, a fatty acid that is institute naturally in various animal and vegetable fats and oils.

CH₃(CH_ii)₇CH=CH(CH₂)_sevenCOOH

Solution

Start by drawing the CH₃. The (CH_two)₇ represents a repeating unit, meaning you must describe seven CH_two'south one subsequently some other, which are bonded to a CH which is bonded to a CH, and then another seven CH_two's. The COOH represent a carboxylic acid, which ways you have a C=O connected to an O-H. Always double check your structure to ensure every carbon is making four bonds. When you do this, you will come across the 2 CH must be double bonded.

Exam Yourself
Common organic compounds that you likely have at home are: acetone (CH₃COCH_three) found in nail smooth remover, acetic acid (CH₃COOH) found in vinegar, and isopropanol ((CH_three)₂CHOH) constitute in rubbing alcohol. Decide the Lewis Structure for each of these household chemicals.

Answer

More unremarkably, organic and biological chemists use an abbreviated drawing convention called line structures, also known as skeletal structures or line bond structures. The convention is quite unproblematic and makes it easier to describe molecules, but line structures do take a little fleck of getting used to. Carbon atoms are depicted not past a capital C, simply by a 'corner' between two bonds, or a free end of a bond. Open-concatenation molecules are usually drawn out in a 'zig-zig' shape. Hydrogens attached to carbons are generally not shown: rather, similar alone pairs, they are simply implied (unless a positive formal charge is shown, all carbons are assumed to have a full octet of valence electrons). Hydrogens bonded to nitrogen, oxygen, sulfur, or anything other than carbon areshown, only are usually drawn without showing the bond. The post-obit examples illustrate the convention.

**Figure 2.** Comparison between Lewis structure and line construction.

As you can see, the 'pared down' line construction makes it much easier to see the basic structure of the molecule and the locations where there is something other than C-C and C-H single bonds. For larger, more complex biological molecules, it becomes impractical to utilise full Lewis structures. Conversely, very small-scale molecules such as ethane should exist fatigued with their total Lewis or condensed structures.

Sometimes, one or more than carbon atoms in a line structure will exist depicted with a capital C, if doing so makes an explanation easier to follow.If you characterization a carbon with a C, you also must draw in the hydrogens for that carbon.

Instance 2

Draw the line structures for these ii molecules:

Solution
Each carbon atom is converted into the finish of a line or the place where lines intersect. All hydrogen atoms fastened to the carbon atoms are left out of the structure (although we yet demand to recognize they are at that place):
Figure a shows a branched skeleton structure that looks like a plus sign with line segments extending up and to the right and down and to the left of the rightmost point of the plus sign. Figure b appears in a zig zag pattern made with six line segments. The segments rise, fall, rise, fall, rise, and fall moving left to right across the figure.

Test Yourself
Describe the line structures for these ii molecules:
Figure a shows five C H subscript 2 groups and one C H group bonded in a hexagonal ring. A C H subscript 3 group appears above and to the right of the ring, bonded to the ring on the C H group appearing at the upper right portion of the ring. In b, a straight chain molecule composed of C H subscript 3 C H subscript 2 C H subscript 2 C H subscript 2 C H subscript 3 is shown.

Answers

Example 3

Identify the chemical formula of the molecule represented here:
This figure shows a pentagon with a vertex pointing right, from which a line segment extends that has two line segments attached at its right end, one extending up and to the right, and the other extending down and to the right.

Solution
At that place are eight places where lines intersect or end, significant that in that location are viii carbon atoms in the molecule. Since nosotros know that carbon atoms tend to make four bonds, each carbon atom will have the number of hydrogen atoms that are required for four bonds. This compound contains 16 hydrogen atoms for a molecular formula of C₈H_sixteen.

Location of the hydrogen atoms:
In this figure a ring composed of four C H subscript 2 groups and one C H group in a pentagonal shape is shown. From the C H group, which is at the right side of the pentagon, a C H is bonded. From this C H, a C H subscript 3 group is bonded above and to the right and a second is bonded below and to the right.

Test Yourself
Place the chemical formula of the molecule represented here:
A skeleton model is shown with a zig zag pattern that rises, falls, rises, and falls again left to right through the center of the molecule. From the two risen points, line segments extend both up and down, creating four branches.