The transformation shown below can be accomplished in TWO reaction steps. From the following list, select the two reagents (or sets of reagents) which would most effectively bring about this conversion. Reagents:

1. Conc H2SO4/heat
2. CN-
3. KMnO4
4. (i) CH3MgI (ii) H3O+
5. PBr3
6. (i) BH3 (ii) H2O2
7. CH3CH2O-/CH3CH2OH
8. H2O/H+
9. OH-/H2O
10. (i) O3 (ii) Zn
11. NaBH4
12. HCl
13. KI
14. Na
15. CH3CH2Br

Please enter the reagent number (from the above list) for each of the two steps in the following synthesis:
Step 1:?
Step 2:?

CH3CH2CHO ->(Step 1) ->(Step 2) CH3-CH=CH-CH3

Thanks a lot

http://en.wikipedia.org/wiki/Grignard_reaction

Look at reagent pair number 4.

To determine the two reagents required to accomplish the given transformation, we need to analyze the reaction steps and identify the appropriate reagents for each step.

Step 1: CH3CH2CHO -> ? -> CH3-CH=CH-CH3

In the given reaction, we can see that the aldehyde (CH3CH2CHO) is being converted into a double bond (CH3-CH=CH-CH3). We can achieve this conversion by performing an oxidation reaction.

Looking at the provided reagents list, we can eliminate reagents that are not known for their oxidizing properties, such as NaBH4, HCl, KI, Na, CH3CH2Br, and all the reagents that are reducing agents (as oxidation is not possible with them).

The most common oxidizing reagents listed are KMnO4 and PBr3. However, KMnO4 is a strong oxidizing agent that would further oxidize the alcohol to a carboxylic acid, which is not the desired product. Therefore, we can eliminate KMnO4.

The remaining suitable reagent for Step 1 is PBr3, which is used for converting alcohols into alkyl halides. In this case, it will convert the alcohol group (-CHOH) of the aldehyde into a bromomethane group (-CHBr), leading to the formation of an alkyl bromide.

So, for Step 1, the appropriate reagent is: PBr3.

Now, let's move on to Step 2.

Step 2: CH3-CHBr-CH3 -> ? -> CH3-CH=CH-CH3

In this step, we can see that the bromomethane (CH3-CHBr-CH3) is being converted into a double bond (CH3-CH=CH-CH3). To accomplish this, we need to perform an elimination reaction.

Among the remaining reagents, we can see that reagents like Conc H2SO4/heat, Na, HCl, and KI are not known for their ability to perform elimination reactions.

The appropriate reagent for an elimination reaction is a strong base. Among the listed reagents, OH-/H2O is a strong base that can eliminate the bromine atom (-Br) from the bromomethane and form a double bond.

Thus, for Step 2, the appropriate reagent is: OH-/H2O.

In summary, the two reagents for the two reaction steps are:
Step 1: PBr3
Step 2: OH-/H2O