CHM 238 Midterm Fall 2026

Substrate

Electrophile (often an alkyl halide) undergoing substitution or elimination

Nucleophile

Donates its electrons to central atoms (i.e. atoms other than H), typically stronger with increasing negative charge

Leaving Group

Atom (or group of atoms) that leave the molecule (i.e. weak bases, halides)

Base

Donates electrons to a H atom

Do alcohols make good substrates for nucleophile reactions? Why/why not? What can be added to speed up the reaction?

No. The hydroxide ion is a strong base and weak bases make beter leaving groups. Acid can be added to speed up the reaction

What are 3 major types of lab protection you must wear at all times in the lab?

Googles, lab coat, and long pants (also long sleeve shirts and close toed shoes)

The notebook must include a list of chemicals. List 2 things that must be included for each chemical.

Melting point and hazards (also structure, molecular formula, boiling point, density, and solubility)

5 Steps of Recrystallization

1. Dissolve solute in a minimum amount of hot solvent

2. Allow to cool to room temp.

3. Scratch inside of the container to indue crystallization

4. Put in ice bath & keep scratching

5. Collect by centrifugation or vacuum filtration

Why was aqueous sodium bicarbonate (NaHCO3) used to wash the extraction mixture in the synthesis of n-butyl bromide?

Aqueous sodium bicarbonate was used to wash the extraction in order to neutralize the leftover chemical mixture.

Draw one possible chemical reactions involved in the previous question.

HCl (aq) + NaHCO3 (aq) → NaCl (aq) + CO2 (g) + H2O (g)

In every synthesis unwanted side products are inevitably formed. 2 different mechanisms led to the unwanted side products during the experiments performed this week. Choose the 2 mechanism types that lead to the undesired contaminants.

Elimination and Substitution

Why would sodium acetate (CH3CO2Na) make a poor soap? Be clear and concise with your answer.

It would make a poor soap because the carbon chain is too short, which in turn will cause the soap to be less soluble.

Which of the following factors can influence the hardness/softness of a soap?

The common ion effect states that adding a common ion to the mixture will shift the equilibrium toward the solid soap, causing the soap to precipitate.

In your own words, describe how soap works.

Soap is made of micelles, which is a compound with hydrophilic heads and hydrophobic tails. Micelles trap dirt inside with the hydrophobic tails while the hydrophilic heads interact with the water. Ince this occurs, the soap is rinsed away and the entire micelle is washed away.

What type of reaction takes place in a condensation polymerization reaction?

Nucleophilic acyl substitution

What type of reaction takes place in an addition polymerization reaction?

Radical addition

One of the polymers you made in the lab was cross-linked and the other was linear. What distinguishing feature indicates that a monomer can be used to form a cross-linked polymer?

Having more than 2 functional groups on the monomer

What technique/method was used in the lab to determine the selectivity of the hypochlorite oxidation?

IR spectroscopy

Which definition is correct for an oxidation reaction?

The removal of hydrogen atoms, and the addition of bonds to more electronegative heteroatoms.

What change would you see in the IR if pentan-1-ol was oxidized to pentanal (the aldehyde)?

The absorbance between 3200-3600 cm^-1 would disappear, an absorbance between 1720-1740 cm^-1 would appear, and two absorbances between 2750-2850 cm^-1 would appear.

Which of the following correctly describes the behavior of a Grignard reagent?

Strong nucleophile

Rank the following according to their strengths as nucleophiles (greatest = strongest nucleophile; least = weakest nucleophile).

Organomagnesium (Grignard) - I

Organocuprate (Gilman) - II

Oranolithium - III

III > I > II

Why does the glassware need to be baked in an oven before performing a Grignard reaction?

Any residual water on the glassware will destroy the Grignard reagent.