[portugal]

Since NaSCH3 is a weak base but a very strong nucleophile this means that alkyl halides undergoes an SN2 substitution rather and elimination is that right or not??

[azmanam]

depends on the alkyl halide

see here

http://www.cem.msu.edu/~reusch/VirtTxtJml/alhalrx3.htm#hal9

[portugal]

well its a primary alkyl halide and therefore its a substitution according to that page is that right?

[azmanam]

yes

[Lonestar]

put simply, SN2 requires the nucleophile to perform a "back side attack" which means it hits the carbon on the side opposite the side bonded to the leaving group, so a primary is good cuase no hinderence to the "back side attack". A tert alkyl halide is bad cuase it'll be all clustered and hindered.

if you got a primary alkyl halide and a strong nucleophile then yeah, most likely SN2 hence, it depends on your alkyl halide

it should be noted that the strength of the nucleophile is not important in an SN1 reaction

[azmanam]

strength of the nucleophile is not important in an S_N1 reaction

unless it is a strong nucleophile AND a strong base, then competing pathways may emerge, depending on the alkyl halide.

now, concentration of nucleophile is not important to the rate of the S_N1.  know why?