DAT Organic Chemistry - Problem Drill 05: Drawing Organic Structures ...

DAT Organic Chemistry - Problem Drill 05: Drawing Organic Structures

Question No. 1 of 10

Instructions: (1) Read the problem statement and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.

Question 1. What does the abbreviation "Ar" stand for?

Question #01

(A) Acetyl group (B) Benzyl group (C) Aromatic or Aryl group (D) Benzoyl group (E) Ethyl group

A. Incorrect! Acetyl groups are abbreviated as "Ac". Go back and review the most common abbreviations used in organic chemistry.

B. Incorrect! Benzyl groups are abbreviated as "Bn". Go back and review the most common abbreviations used in organic chemistry.

Feedback on Each Answer Choice

C. Correct! The abbreviation "Ar" stands for an aromatic ring, sometimes called an aryl ring.

D. Incorrect! Benzoyl groups are abbreviated as "Bz". Go back and review the most common abbreviations used in organic chemistry.

E. Incorrect! Ethyl groups are abbreviated as "Et". Go back and review the most common abbreviations used in organic chemistry.

(1) Recall the common organic abbreviations.

You will need to know the abbreviations and the structures they represent. Ar is the abbreviation for an aromatic ring (also called an aryl ring.)

Therefore, the correct answer is (C).

Solution

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Question No. 2 of 10

Instructions: (1) Read the problem statement and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.

Question 2. What abbreviation would be used for the following structure?

O

Question #02

(A) Bn (B) Ac (C) Py (D) Bz (E) Ph

A. Incorrect! The abbreviation "Bn", which stands for a benzyl group, describes a structure where a benzene ring is bonded to a CH2 (methylene) group. Go back and review the common abbreviations used in organic chemistry.

B. Incorrect! The abbreviation "Ac", which stands for an acetyl group, describes a structure where a methyl group is bonded to a carbonyl. Go back and review the common abbreviations used in organic chemistry.

Feedback on Each Answer Choice

C. Incorrect! The abbreviation "Py", which stands for a pyridine ring, describes a six-membered aromatic ring where one of the atoms in the ring is nitrogen. Go back and review the common abbreviations used in organic chemistry.

D. Correct! The structure pictured above is a benzoyl group which is abbreviated as "Bz".

E. Incorrect! The abbreviation "Ph" stands for a phenyl group. Go back and review the common abbreviations used in organic chemistry.

(1) Recall the common organic abbreviations.

You will need to know the abbreviations and the structures they represent. This structure containing a carbonyl bonded to an aromatic ring is known as a benzoyl group. Its abbreviation is "Bz".

Therefore, the correct answer is (D).

Solution

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Question No. 3 of 10

Instructions: (1) Read the problem statement and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.

Question 3. What kind of structure appears below?

Question #03

(A) Lewis structure (B) Skeletal structure (C) Sawhorse structure (D) Condensed structure (E) None of the above.

CH3CH2CH2CH2OH

Feedback on Each Answer Choice

A. Incorrect! In a Lewis structure, all individual bonds and nonbonding electron pairs are shown. In the above structure, no bonds or lone pairs are explicitly drawn. Go back and review the different types of structures that can be used to illustrate organic compounds.

B. Incorrect! In a skeletal structure, lines represent bonds and carbon atoms are assumed to be where two lines meet or at the end of a line. Hydrogens are not shown. Go back and review the different types of structures that can be used to illustrate organic compounds.

C. Incorrect! In a sawhorse structure, the molecule is drawn so that one is looking down a carbon-carbon bond. Go back and review the different types of structures that can be used to illustrate organic compounds.

D. Correct! In a condensed structure, atoms bonded to a single atom are listed after the atom. No bonds are explicitly drawn.

Solution

E. Incorrect! The correct answer is in the above choices. Go back and review the different types of structures that can be used to illustrate organic compounds.

(1) Recall the different types of structures that may be drawn to represent an organic compound.

Lewis structures show all individual atoms and nonbonding pairs of electrons. They are drawn using the valence electrons of the compound and show most, if not all, bonds explicitly.

Condensed structures are more like a shorthand version of Lewis structures with atoms bonded to one atom being shown after that atom. Bonds are not typically shown in a condensed structure.

Skeletal structures are an even quicker way of drawing a structure. In a skeletal structure, carbon and hydrogen atoms are not explicitly drawn. Carbons are assumed to be at the point where two lines, representing bonds, meet or at the end of such a bond. Heteroatoms (atoms that are not carbon or hydrogen) are shown as are any nonbonding pairs of electrons. Hydrogens, however, are not shown. If a carbon is shown with less than 4 bonds, it is assumed that the remaining atoms bonded to it are hydrogens. This is the most common structure used when drawing organic compounds.

Sawhorse structures are drawn as to give a more three-dimensional look to the structure. They are drawn looking down a carbon-carbon bond in the molecule. Which carbon-carbon bond used may vary.

(2) Look at the structure above and determine what kind of structure it is.

This structure is drawn by showing atoms bonded to one atom being shown after that atom. No bonds are explicitly drawn. It must be a condensed structure.

Therefore, the correct answer is (D).

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Question No. 4 of 10

Instructions: (1) Read the problem statement and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.

Question 4. What kind of structure is shown below?

HHHH

HCCCCH

HHHH

Question #04

(A) Lewis structure (B) Condensed structure (C) Sawhorse structure (D) Skeletal structure (E) Ionic structure

A. Correct! This structure is drawn using the valence electrons of the compound. Bonds are explicitly shown so it must be a Lewis structure.

Feedback on Each Answer Choice

B. Incorrect! Condensed structures are a shortened version of Lewis structures with atoms bonded to one atom being shown after that atom. Bonds are not typically shown in a condensed structure. Here, the bonds are drawn out so it can not be a condensed structure. Go back and review the different types of structures used to represent organic compounds.

C. Incorrect! Sawhorse structures are drawn to give the structure a more three-dimensional look by drawing it as though one was looking down a carbon-carbon bond in the molecule. This is a very flat representation of a molecule so it can not be a sawhorse structure. Go back and review the different types of structures used to represent organic compounds.

D. Incorrect! In a skeletal structure, carbon and hydrogen atoms are not explicitly drawn. In the above structure, all carbons and hydrogens are shown. Go back and review the different types of structures used to represent organic compounds.

Solution

E. Incorrect! Ionic structures refer to compounds composed of a metal and nonmetal (salt) that bond through the complete transfer of electrons between atoms. Go back and review the different types of structures used to represent organic compounds.

(1) Recall the different types of structures that may be drawn to represent an organic compound.

Lewis structures show all individual atoms and nonbonding pairs of electrons. They are drawn using the valence electrons of the compound and show most, if not all, bonds explicitly.

Condensed structures are more like a shorthand version of Lewis structures with atoms bonded to one atom being shown after that atom. Bonds are not typically shown in a condensed structure.

Skeletal structures are an even quicker way of drawing a structure. In a skeletal structure, carbon and hydrogen atoms are not explicitly drawn. Carbons are assumed to be at the point where two lines, representing bonds, meet or at the end of such a bond. Heteroatoms (atoms that are not carbon or hydrogen) are shown as are any nonbonding pairs of electrons. Hydrogens, however, are not shown. If a carbon is shown with less than 4 bonds, it is assumed that the remaining atoms bonded to it are hydrogens. This is the most common structure used when drawing organic compounds.

Sawhorse structures are drawn as to give a more three-dimensional look to the structure. They are drawn looking down a carbon-carbon bond in the molecule. Which carbon-carbon bond used may vary.

(2) Look at the structure above and determine what kind of structure it is.

This structure is drawn using the valence electrons of the compound. The bonds are explicitly drawn. It must be a Lewis structure.

Therefore, the correct answer is (A).

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Question No. 5 of 10

Instructions: (1) Read the problem statement and answer choices carefully (2) Work the problems on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.

Question 5. How many carbons are in the skeletal structure below?

Cl

Question #05

OH

(A) 6 (B) 8 (C) 10 (D) 12 (E) 14

A. Incorrect! There are more than 6 carbons in the skeletal structure above. Remember, carbons are assumed to be anywhere a line ends or where two lines meet (at the vertices).

B. Incorrect! There are more than 8 carbons in the skeletal structure above. Remember, carbons are assumed to be anywhere a line ends or where two lines meet (at the vertices).

Feedback on Each Answer Choice

C. Correct! Carbons are assumed to be anywhere a line ends or where two lines meet. There are 10 carbons in this structure.

D. Incorrect! There are less than 12 carbons in the skeletal structure above. Remember, carbons are assumed to be anywhere a line ends or where two lines meet (at the vertices).

E. Incorrect! There are less than 14 carbons in the skeletal structure above. Remember, carbons are assumed to be anywhere a line ends or where two lines meet (at the vertices).

Solution

(1) Recall what the tutorial said about skeletal structures.

In a skeletal structure, carbon and hydrogen atoms are not explicitly drawn. Carbons are assumed to be at the point where two lines, representing bonds, meet or at the end of such a bond. Heteroatoms (atoms that are not carbon or hydrogen) are shown as are any nonbonding pairs of electrons. Hydrogens, however, are not shown. If a carbon is shown with less than 4 bonds, it is assumed that the remaining atoms bonded to it are hydrogens.

(2) Study the structure and count the number of carbons it contains.

Number all the carbons in the structure below. Remember, carbons are assumed to be at the point where two lines, representing bonds, meet or at the end of such a bond.

Cl

1 2 345 6 7

8 10

9 OH

Therefore, the correct answer is (C).

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