We report on measurements of the neutron spin asymmetries A n 1,2 and polarized structure functions g n 1,2 at three kinematics in the deep inelastic region, with x = 0.33, 0.47 and 0.60 and Q 2 = 2.7, 3.5 and 4.8 (GeV/c) 2 , respectively. These measurements were performed using a 5.7 GeV longitudinally-polarized electron beam and a polarized 3 He target. The results for A n 1 and g n 1 at x = 0.33 are consistent with previous world data and, at the two higher x points, have improved the precision of the world data by about an order of magnitude. The new A n 1 data show a zero crossing around x = 0.47 and the value at x = 0.60 is significantly positive. These results agree with a next-to-leading order QCD analysis of previous world data. The trend of data at high x agrees with constituent quark model predictions but disagrees with that from leading-order perturbative QCD (pQCD) assuming hadron helicity conservation. Results for A n 2 and g n 2 have a precision comparable to the best world data in this kinematic region. Combined with previous world data, the moment d n 2 was evaluated and the new result has improved the precision of this quantity by about a factor of two. When combined with the world proton data, polarized quark distribution functions were extracted from the new g n 1 /F n 1 values based on the quark parton model. While results for ∆u/u agree well with predictions from various models, results for ∆d/d disagree with the leading-order pQCD prediction when hadron helicity conservation is imposed.