Workshop Chapter 2 KEY PDF

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CHM 2210 Workshop Chapter 2 Practice of Learning Objectives (LOs) – Exam 1 All exercises are in addition to the text questions assigned. You will master the material by applying the material and answering questions on it. Chapter 2 LO1. Convert between Lewis structures, partially condensed structures, condensed structures, and bond-line structures a. Fill in the blanks. Articulate a summary of what you have learned. The molecular formula does not provide structural information. Chemists use many different drawing styles to communicate structural information, including Lewis structures, condensed structures, and bond-line structures. To show a molecule is 3-D, a saw-horse style is commonly used where a dashed (or hashed) wedge represents a group going ___into___ the page and a solid bold wedge represents a group coming _out____ of the page. In another type of representation known as skeletal, bond-line, or bond-angle structures, the___carbon___ atoms and most ___hydrogen______ atoms are not shown. Bond-line structures are much faster to draw and easier to interpret than the other drawing styles. These will be used throughout the rest of Organic I & II, so it is important to understand them extremely well. Lone pairs are often not drawn in bond-line structures. It is important to recognize that these lone pairs are present. b. Write the best Lewis (or Kekulé) structure (use lines for bonds and show all lone pairs) for each of the following molecules given as condensed structures. HCCH CH2CHOH CH3COOCH3

c. Provide the best bond-line structures for each of the following condensed structures. (Hint: show all lone pair electrons) (CH3) 3COH NH2CH(CH3) 2 CH3NHCH(CH3) 2

LO2. Identify and draw the functional groups a. ‘__Functional_____ groups’ are groups of atoms/bonds that have predictable chemical behavior. The chemistry of every organic compound is determined by the functional groups present in the compound. b. Name the circled functional groups.

a.__aldehyde____________________________________ c.__carboxylic acid________________________________ e.__ amine______________________________________ g.__ alkyne______________________________________ i.___alkene_____________________________________

b.__ketone___________________________________ d.__ester_____________________________________ f.__ amide ____________________________________ h.__ alcohol___________________________________ j.___acid halide________________________________

A.______ alcohol____________________________

E.________carboxylic acid______________________

B.______ alcohol____________________________

F.________ amide_____________________________

C.______aromatic or arene_____________________

G.________ketone_____________________________

D. ____nitrile________________________________

H.________ether______________________________

d. A fun game to learn many of the functional groups! Within each row, column, and bolded 9 box cube – you cannot use the same functional group more than once. Use inclusive (it must be there because) and exclusive (it cannot be there because) reasoning to fill in the rest of the Sudoku puzzle! The 9 functional groups found in the puzzle are: acid chloride, alcohol, aldehyde, alkene, amine, amide, carboxylic acid, ester, ketone.

Organic Sudoku Acid chloride

Carb acid

H

Ester

Amine

Alcohol

Ketone

H

Aldehyde

Amide H

CH3-NH 2

Aldehyde O

Amide R

R

Alkene OH | CH 3-C-CH 3 | CH 3

CH 3CH 2COOH

Amine

Acid Chl.

O

H3C

NH2

Acid Chl.

O

Ketone

Alcohol

Ester

Alkene

R

R O

O

H3C

Acid Chl.

O

H3C

Ester

CH3

H

O

OH

OH

O

R

Amine

H H3C

Ketone

H3C

H

Alkene

H3C

Amide OH

O

Amide Aldehyde

Alcohol H3C

Cl

O

O CH3

CH2 COOCH3

H3C

Carb. Acid

Alkene H3C

R-COOH

Alkene

Carbo xy lic Acid

R

CH3 CONH2

Alcohol CH2 =CH2

Ketone

Amine

Aldehyde

Acid Chl.

Alcohol

Acid Chl.

OH | CH 3CHCH 3

CH3

Aldehyde

Ketone

NH2 | CH 3CHCH 3

H

Amide

Ester

O

O

Cl

R-NH2

Ketone

R-OH

Amine

Aldehyde

Carb acid

H3C

O R NH2

Alkene

CH3 H

Ester

Aldehyde

Amine

CH 3COCH 3

Amide

Ester

Carb Acid

Acid Chl.

LO3. Identify lone pairs and formal charges in bond-line structures a. Draw in the missing hydrogens and lone pairs on this line-angle structure.

LO4. Explain resonance stabilization and electron delocalization a. Fill in the blanks. Articulate a summary of what you have learned. Localized electrons exhibit normal lone pair or pi bond behavior. A localized lone pair remains close to one atom. A localized double bond’s electrons are shared covalently between two atoms. Through resonance, electrons are delocalized over 3 or more adjacent p orbitals in a Pi system. Delocalized electrons are the electrons in a molecule, ion, or solid metal that are not associated with a single atom or a covalent bond. When a single Lewis structure doesn’t properly represent the true charge or bonding nature, then ___resonance____ structures are used. In organic chemistry, it typically refers to an extended overlap of the pi system through which electrons can be delocalized, which stabilizes or distributes charge and lowers the energy of molecules. Resonance structures are separated by double-headed arrows and surrounded by brackets. All formal charges are shown. Resonance structures contribute to the resonance hybrid which is a better representation of the true nature of the molecule. Two basic resonance rules: 1) never exceed an __octet_____ for second row elements and 2) never break a single (sigma) bond. Since resonance is redistributions of electrons through the pi system, the atoms don’t move. Resonance structures are most easily drawn by looking for the following five patterns: 1. An allylic lone pair 2. An allylic carbocation 3. A lone pair adjacent to C+ 4. A π bond between two atoms of differing electronegativity 5. Conjugated π bonds enclosed in a ring b. There is something wrong with some of the resonance structures shown below. Briefly detail WHY the 2nd resonance structure has an error OR write N/A if there isn’t an error.

LO5. Use curved arrows to draw resonance structures Curved arrows are drawn to show the electron flow needed to achieve the next resonance structure. When drawing resonance structures, always begin by looking for the patterns that utilize only one curved arrow. a. Provide the structure for the resonance contributor by following the electron flow shown by the electron arrows given.

LO6. Compare the significance of different resonance structures a. Fill in the blanks. Articulate a summary of what you have learned. The best contributor is found by: 1) maximizing __octets____; the most significant resonance forms have the greatest number of filled octets. 2) minimizing __charge____ ; the structure with fewer formal charges is more significant. 3) considering electronegativity by placing a negative charge on a more electronegative atom when a negative charge is present (or a positive charge on a less electronegative atom provided the number of octets isn’t reduced). Resonance forms that have equally good Lewis structures are described as equivalent and contribute equally to the resonance hybrid. When resonance structures are not electronically equal, one will make a greater contribution to the resonance hybrid. Whenever an atom possesses both a π bond and a lone pair, they will not both participate in resonance. b. Draw the electron arrows for each step, the resulting structures, and circle the major contributor.

LO7. Construct a resonance hybrid for a set of resonance structures a. Fill in the blanks. Articulate a summary of what you have learned. Resonance structures collectively represent only one entity. This entity, often called the resonance hybrid, is a combination of the individual Lewis resonance structures. A resonance hybrid can be drawn by using partial bonds and partial charges to illustrate the delocalization of electrons. b. The molecule shown below has some important resonance contributors. Provide three additional resonance structures and include the electron arrows needed to generate the proper electron flow to the next resonance contributor in the sequence.

c. Consider your resonance structures from b. Draw the structure that contributes most to the resonance hybrid

d. Finish drawing the resonance hybrid showing the presence of partial bonds and partial charges. e. Label the most nucleophilic atom (electron-rich) and the most electrophilic atom (electron-poor).

f. The molecule shown below has some important resonance contributors. Provide two additional resonance structures and include the electron arrows needed to generate the proper electron flow to the next resonance contributor in the sequence.

g. Consider your resonance structures from f. Draw the structure that contributes most to the resonance hybrid

h. Finish drawing the resonance hybrid showing the presence of partial bonds and partial charges. i. Label the most nucleophilic atom (electron-rich) and the most electrophilic atom (electron-poor).

LO8. Distinguish between delocalized and localized lone pairs in a structure a. Draw in the missing hydrogens and lone pairs. Then, determine what the hybridization is for each atom in the whole structure. Don’t forget resonance’s influence on hybridization – delocalize the lone pairs next to pi systems!...